Clean up some loose ends.
- Add float 32 and 64 parsing.
- Do integer parsing correctly.
- Support string escaping.
- Fix some definitions, e.g. limit definition of whitespace to capnp definition.
Fix default value parsing which also allows for struct values as annotation arguments.
Further cleanups and a little more testing.
Clean up code some more.
Encode some more grammar rules as enforced by capnp.