src: Use UnicodeError instead of UnicodeDecodeError ...

MicroPython doesn't support UnicodeDecodeError, just UnicodeError.

src: Check for None in all __eq__ methods ...

This lets us finally compare parse error exceptions and contexts of
different shapes.

syntax: Drop NewLang version keyword ...

Bundling NewLang solves the issue of version compatibility.

syntax: Drop support for shebangs ...

Shebangs are useful for writing scripts, but they assume an install of
NewLang separate from the application.

I don't plan to support that, only bundling of NewLang and its scripts.

parse: Move to oldparse ...

This is in preparation of writing a new parser.
Once the new parser is ready then this code can be junked.