env: Fix mutmut paths

Jenkinsfile: Fix build

gitignore: Ignore build/ directory

README: Install and run guide

src: Set exe_name to 'newlang' unconditionally

build: Switch to regular Python building

requirements: Drop unused grip dependency ...

Apparently I forgot to add grip support to env.sh and only noticed now.
I'm not using it so just remove it.

main: Allow passing exe_name for better looking output

src: Move run.py to __main__.py ...

This allows running NewLang as a Python module.

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.

env: Clean up run.py also

env: Pass --use-pep517 to pip ...

I don't fully understand this, but we need to do this now.

More reading:

https://blog.ganssle.io/articles/2021/10/setup-py-deprecated.html

I'm not sure exactly

env: Fix and simplify mutmut mutating ...

Instead of passing individual files, just parse the parse2 directory.
Make sure to do this on Windows too.

parse: Rename oldparse back to parse ...

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

parse2: Move all new parser code to the parse2 namespace ...

This is a bit of a messy mass rename but it seems to work and makes things
clearer in preparation for a new parse module.

This also renames the NEWLANG_NEW_PARSE test environment variable to
NEWLANG_PARSE2.

tests: Add more test_note documentation

tests: Add more clear_notes documentation

parse: Take parse_file out of Parser wrapper

parse: Drop NoteSkipper wrapper class

tests: Fix invalid directive comments

tests: Check clear_notes error passthrough

tests: Replace file parsing mock with static directives

tests: Simplify clear_notes tests ...

This replaces mocking static tests and assumes errors are parsed
through because the actual parser is triggered.

flake8: Ignore some useless errors

env: Add resetenv command ...

This is useful for refreshing installed packages.

env.sh: Don't quit shell on error ...

This current behaviour doesn't leave time for error messages or
rectifying the issue. Just return instead.

requirements: Unlock hypothesis ...

After a ton of refactoring newer hypothesis versions are now happy to
work without warning again. I hope.

tests: Wrap test_oldparse's draw_token_empty in just

tests: Remove unused template_parse_* functions

tests: Don't return old tokens in draw_token_statement_invalid_value