Upgrade doxygen to 1.9.6 (#163)

Doxygen 1.9.5 can report false positives
around function parameters. 1.9.6 does not
have this bug.

docs/doxygen/config.doxyfile

@@ -1,4 +1,4 @@
-# Doxyfile 1.9.5
+# Doxyfile 1.9.6
 
 # This file describes the settings to be used by the documentation system
 # doxygen (www.doxygen.org) for a project.
@@ -86,7 +86,7 @@ CREATE_SUBDIRS         = NO
 # level increment doubles the number of directories, resulting in 4096
 # directories at level 8 which is the default and also the maximum value. The
 # sub-directories are organized in 2 levels, the first level always has a fixed
-# numer of 16 directories.
+# number of 16 directories.
 # Minimum value: 0, maximum value: 8, default value: 8.
 # This tag requires that the tag CREATE_SUBDIRS is set to YES.
 
@@ -568,7 +568,8 @@ HIDE_UNDOC_MEMBERS     = NO
 # If the HIDE_UNDOC_CLASSES tag is set to YES, doxygen will hide all
 # undocumented classes that are normally visible in the class hierarchy. If set
 # to NO, these classes will be included in the various overviews. This option
-# has no effect if EXTRACT_ALL is enabled.
+# will also hide undocumented C++ concepts if enabled. This option has no effect
+# if EXTRACT_ALL is enabled.
 # The default value is: NO.
 
 HIDE_UNDOC_CLASSES     = NO
@@ -859,6 +860,14 @@ WARN_IF_INCOMPLETE_DOC = YES
 
 WARN_NO_PARAMDOC       = NO
 
+# If WARN_IF_UNDOC_ENUM_VAL option is set to YES, doxygen will warn about
+# undocumented enumeration values. If set to NO, doxygen will accept
+# undocumented enumeration values. If EXTRACT_ALL is set to YES then this flag
+# will automatically be disabled.
+# The default value is: NO.
+
+WARN_IF_UNDOC_ENUM_VAL = NO
+
 # If the WARN_AS_ERROR tag is set to YES then doxygen will immediately stop when
 # a warning is encountered. If the WARN_AS_ERROR tag is set to FAIL_ON_WARNINGS
 # then doxygen will continue running as if WARN_AS_ERROR tag is set to NO, but
@@ -1182,46 +1191,6 @@ USE_HTAGS              = NO
 
 VERBATIM_HEADERS       = YES
 
-# If the CLANG_ASSISTED_PARSING tag is set to YES then doxygen will use the
-# clang parser (see:
-# http://clang.llvm.org/) for more accurate parsing at the cost of reduced
-# performance. This can be particularly helpful with template rich C++ code for
-# which doxygen's built-in parser lacks the necessary type information.
-# Note: The availability of this option depends on whether or not doxygen was
-# generated with the -Duse_libclang=ON option for CMake.
-# The default value is: NO.
-
-CLANG_ASSISTED_PARSING = NO
-
-# If the CLANG_ASSISTED_PARSING tag is set to YES and the CLANG_ADD_INC_PATHS
-# tag is set to YES then doxygen will add the directory of each input to the
-# include path.
-# The default value is: YES.
-# This tag requires that the tag CLANG_ASSISTED_PARSING is set to YES.
-
-CLANG_ADD_INC_PATHS    = YES
-
-# If clang assisted parsing is enabled you can provide the compiler with command
-# line options that you would normally use when invoking the compiler. Note that
-# the include paths will already be set by doxygen for the files and directories
-# specified with INPUT and INCLUDE_PATH.
-# This tag requires that the tag CLANG_ASSISTED_PARSING is set to YES.
-
-CLANG_OPTIONS          =
-
-# If clang assisted parsing is enabled you can provide the clang parser with the
-# path to the directory containing a file called compile_commands.json. This
-# file is the compilation database (see:
-# http://clang.llvm.org/docs/HowToSetupToolingForLLVM.html) containing the
-# options used when the source files were built. This is equivalent to
-# specifying the -p option to a clang tool, such as clang-check. These options
-# will then be passed to the parser. Any options specified with CLANG_OPTIONS
-# will be added as well.
-# Note: The availability of this option depends on whether or not doxygen was
-# generated with the -Duse_libclang=ON option for CMake.
-
-CLANG_DATABASE_PATH    =
-
 #---------------------------------------------------------------------------
 # Configuration options related to the alphabetical class index
 #---------------------------------------------------------------------------
@@ -1233,10 +1202,11 @@ CLANG_DATABASE_PATH    =
 
 ALPHABETICAL_INDEX     = YES
 
-# In case all classes in a project start with a common prefix, all classes will
-# be put under the same header in the alphabetical index. The IGNORE_PREFIX tag
-# can be used to specify a prefix (or a list of prefixes) that should be ignored
-# while generating the index headers.
+# The IGNORE_PREFIX tag can be used to specify a prefix (or a list of prefixes)
+# that should be ignored while generating the index headers. The IGNORE_PREFIX
+# tag works for classes, function and member names. The entity will be placed in
+# the alphabetical list under the first letter of the entity name that remains
+# after removing the prefix.
 # This tag requires that the tag ALPHABETICAL_INDEX is set to YES.
 
 IGNORE_PREFIX          =
@@ -1315,7 +1285,12 @@ HTML_STYLESHEET        =
 # Doxygen will copy the style sheet files to the output directory.
 # Note: The order of the extra style sheet files is of importance (e.g. the last
 # style sheet in the list overrules the setting of the previous ones in the
-# list). For an example see the documentation.
+# list).
+# Note: Since the styling of scrollbars can currently not be overruled in
+# Webkit/Chromium, the styling will be left out of the default doxygen.css if
+# one or more extra stylesheets have been specified. So if scrollbar
+# customization is desired it has to be added explicitly. For an example see the
+# documentation.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
 HTML_EXTRA_STYLESHEET  = ./docs/doxygen/style.css
@@ -1331,17 +1306,13 @@ HTML_EXTRA_STYLESHEET  = ./docs/doxygen/style.css
 HTML_EXTRA_FILES       =
 
 # The HTML_COLORSTYLE tag can be used to specify if the generated HTML output
-# should be rendered with a dark or light theme. Default setting AUTO_LIGHT
-# enables light output unless the user preference is dark output. Other options
-# are DARK to always use dark mode, LIGHT to always use light mode, AUTO_DARK to
-# default to dark mode unless the user prefers light mode, and TOGGLE to let the
-# user toggle between dark and light mode via a button.
-# Possible values are: LIGHT Always generate light output., DARK Always generate
-# dark output., AUTO_LIGHT Automatically set the mode according to the user
-# preference, use light mode if no preference is set (the default)., AUTO_DARK
-# Automatically set the mode according to the user preference, use dark mode if
-# no preference is set. and TOGGLE Allow to user to switch between light and
-# dark mode via a button..
+# should be rendered with a dark or light theme.
+# Possible values are: LIGHT always generate light mode output, DARK always
+# generate dark mode output, AUTO_LIGHT automatically set the mode according to
+# the user preference, use light mode if no preference is set (the default),
+# AUTO_DARK automatically set the mode according to the user preference, use
+# dark mode if no preference is set and TOGGLE allow to user to switch between
+# light and dark mode via a button.
 # The default value is: AUTO_LIGHT.
 # This tag requires that the tag GENERATE_HTML is set to YES.
 
@@ -1771,8 +1742,8 @@ MATHJAX_RELPATH        = https://cdn.jsdelivr.net/npm/mathjax@2
 
 # The MATHJAX_EXTENSIONS tag can be used to specify one or more MathJax
 # extension names that should be enabled during MathJax rendering. For example
-# for MathJax version 2 (see https://docs.mathjax.org/en/v2.7-latest/tex.html
-# #tex-and-latex-extensions):
+# for MathJax version 2 (see
+# https://docs.mathjax.org/en/v2.7-latest/tex.html#tex-and-latex-extensions):
 # MATHJAX_EXTENSIONS = TeX/AMSmath TeX/AMSsymbols
 # For example for MathJax version 3 (see
 # http://docs.mathjax.org/en/latest/input/tex/extensions/index.html):