docs: Docs pass for 0.1

[kylebarron]

Change list

• Updated README.md, written by me by hand.
• Added new types that were missing and didn't have an interlink (e.g. Selection, AxisSelector, SupportsDLPack).
• Reduced duplication of type definitions across type hints and python source, e.g. for codecs
• Used show_root_heading: false which makes it look nice to document an entire module in a markdown file. E.g. look in codec.md.
• Imports exceptions into scope in relevant files so that Raises sections can interlink
• Fix formatting of Returns: block, so that it's all kept in a single return render
• New Claude skill for auditing docs, which should be done in advance of every release (and claude will probably use automatically when adding new methods)