Add documentation: provide formatted docstrings for all functions

[msyriac]

There are two ways you can contribute to documentation.

Usage guide

Open docs/usage.rst and start describing how you would carry out commonly done map manipulation tasks. A skeleton structure already exists.

Docstrings

Dig into each module and either edit existing function docstrings or add to empty ones. Try to adapt the docstrings to conform to ReStructured Text (RST) format. Try to add examples that can be understood by doctest.

You can preview docs on your computer before pushing to the repo by doing

cd docs
make html
firefox _build/html/index.html

[mhasself]

Please note that the current "Developer's Guide" recommends "Google" format for docstrings. This is based on the desire that the docstrings render nicely in all of:

• python's built-in "help()"
• the raw source code text
• on sphinx / readthedocs