parse: Add Set node parse code ...

I've taken a different approach this time with my tests by avoiding
decorated functions where I can and adding big upfront documentation
about how things work.

I've deprecated the old decorated functions and hopefully will remove
them during a refactor and cleanup.

parse: Add statement parsing

parse: Parse a reference node

parse: Parse text and bools to AST types

Change license to LGPL-2.1-only

src: Reformat using black

Restructure files