More docs

[grigi]

Wrote a lot more docs.

I'm going to have to pause here for a while. I mostly wrote the docs to help myself understand the project better. Even with the few TODO's littered around the docs are significantly better already.

You can browse them locally by running make devdocs if you want to see.

Done:

• Updated the docstrings to be parseable whilst keeping the syntax human readable
• Added docstrings where I thought it would be needed
• Added changelog (incomplete, only goes back to 0.6.0)
  Placed CHANGELOG.md in the project root and referenced it so we don't have duplications and hopefully it's easy to spot.
• Improved docs landing page
• Improved docs layout
• Added Usage section that has guides on different subjects
• Noted where I feel docs are needed but I didn't get round to it