Reorganize the documentation

[kalekundert]

Here are the some of the things I was trying to address:

• I like having a more clear distinction between the "Getting Started" and "Reference" sections of the documentation. I think the best way to do this is to have separate toc trees with captions.

• I think it's helpful to have "dictionary", "list", and "string" sections in the introduction to the file format, for a couple reasons:

  • It emphasizes the structure of the file format.
  • It helps keep each section focused on one thing.
  • It makes it easy to quickly jump the information you want.

• I think autosummary makes the API documentation easier to navigate. This also entails putting all of the relevant API documentation in the docstrings, which I consider good practice.

[KenKundert]

I have integrated all your suggested changes.