Improve parsing of escaped double quotes

Per the RFC, "" is treated as an escaped quote.
Unfortunately this leads to quoted empty cells, e.g. "","","" being treated as escaped quotes instead of empty cells.

A more careful reading of the spec indicates that this is only valid when already inside double quotes, and the parser has been updated to reflect this.

Also updates the readme to clarify that quoted newlines in cells are not supported.

README.md

@@ -14,7 +14,7 @@ Using NumPy (http://www.numpy.org), the plugin supports evaluating Python expres
 
 All the above features work in both justified and collapsed modes.
 
-Finally, the plugin has full support for RFC 4180 quoting.
+Finally, the plugin fully supports RFC 4180 (https://tools.ietf.org/html/rfc4180) quoting, with the exception that quoted newlines (2.6) are treated as row separators.
 
 ## Install
 

csvplugin.py

@@ -307,24 +307,20 @@ def ParseRow(self, row):
         while char_index < len(row):
             char = row[char_index]
 
-            if char_index < len(row) - 1:
-                next_char = row[char_index + 1]
-            else:
-                next_char = None
-
-            if char == '"' and next_char == '"':
-                if self.auto_quote:
-                    currentword += '"'
-                else:
-                    currentword += '""'
-                char_index += 2
-                continue
-
             if insidequotes:
                 if char == '"':
+                    if char_index < len(row) - 1 and row[char_index + 1] == '"':
+                        if self.auto_quote:
+                            currentword += '"'
+                        else:
+                            currentword += '""'
+                        char_index += 2
+                        continue
+
                     insidequotes = False
                     if not self.auto_quote:
                         currentword += char
+
                 else:
                     currentword += char
 

quote.csv

@@ -0,0 +1,4 @@
+a,"b """,456
+,b
+123abc,"45,6"
+"","",""