src: Move all source code to src/newlang ...

The Python ecosystem works much better if we deicide our source code
is actually a module named 'newlang'.

I've been putting off changing this for a long time, but I might as
well do it now.

parse: Rename oldparse back to parse ...

This is the primary actually working parser, not an old one.

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.

tests: Add SPDX license headers

tests: parser: Remove unused includes ...

Found by flake8.

parse: Strip whitespace in text tokens

parse: Replace 'Begin' with 'Start' in keywords ...

Okay, it's to the point I'm writing bugs in tests due to this.
Just change it already.

tests: Add regression test for trailing whitespace in text

parse: Fix text literals being cut off when placed at end of file

parse: Account for EOF when checking for whitespace ...

When parsing a file that doesn't end with whitespace (like a new line),
the parser would choke on having no symbols left. Fix that.

Fixes: 1519cef