API docs: include multiple versions: master, latest & past releases

[HannoSpreeuw]

• Configure Sphinx
• add API docs
• deploy to RTD/GH pages
• Include a list of all configurable variables, i.e. everything that can be included in a config.toml.
• Make sure that the descriptions of those variables, such as these, are also rendered.
• Indicate clearly which variables will have an effect only for the command line, such as rmsmap; setting this to True has no effect unless the cli is used. residuals and islands, on the other hand, should also be effectuated when not using the cli, since they are propagated here and here, respectively.

[HannoSpreeuw]

Perhaps you could work from documentation_through_Sphinx, although it has little more than master, i.e.

Sphinx boilerplate from running "sphinx-quickstart".

README added to _index.rst_ and uncommenting
import os
import sys
sys.path.insert(0, os.path.abspath('../..'))

such that README.rst is picked up from the top level folder.

[HannoSpreeuw]

Perhaps I should rebase that branch to include the recent updates of master unless you have already pulled it.

[suvayu]

Please rebase it

[HannoSpreeuw]

Okay done and (force) pushed.

[HannoSpreeuw]

Okay done and (force) pushed.

And merged with master as per #142