Documentation Improvements

[ajmedford]

Documentation is currently available at catmap.readthedocs.org, but a number of issues still exist. Feel free to break some of these out into separate issues if you want to work on them.

Add docstrings to all functions

• If you are working on documenting a file please make sure other developers know to avoid overlap.

Fix conversion of tutorials, topics from markdown to rst for readthedocs:

• Links are broken in tutorials
• Some images are missing in topics

Add new tutorials and topics:

• Plotting free energy diagrams
• Plotting scaling relations
• Discussion of situation where there are multiple and/or trivial solutions that must be removed

Add "Examples" section:

• Place to collect examples, similar to Matplotlib gallery. Users (and developers) can include the .mkm file, energy input table, and .py file used to generate various activity/selectivity maps. Include citations so that people can properly cite your work.