parse: Drop enum class in favor of DIY method ...

This is slightly sketchy but should be enough to get MicroPython working
with the new parser.

src: Use UnicodeError instead of UnicodeDecodeError ...

MicroPython doesn't support UnicodeDecodeError, just UnicodeError.

main: Use new parser if NEWLANG_NEW_PARSE is set ...

This is not intended to be actually used outside testing compatibility
with micropython as we don't actually have tests on it yet.

parse: Create messages from ParseTasks

parse: Add filename to error messages

parse: Create messages from ParseErrors

parse: Rename ParseError messages to ParserError

parse: Don't generate message ids, use a table ...

I've decided that all translation strings should be used in source code
as-is without any kind of building.

parse: Add function to fully format an error

parse: Add function to format a ParseContext for display

parse: Add function to format a ParseErrorException for display

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

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

main: Put executable name in usage

main: Add run_file function for REPL use ...

This should help using NewLang from micropython.

log: Rely on main for the getenv call ...

micropython on the Pi Pico for some reason doesn't support getenv, so
try and push this in to main where we can decide to use it.

main: Remove unused nowait_main function

port: Add micropython-compatible atexit wrapper

run: Use run.py to run src/main.py ...

This completely removes the weird logic for editing paths at the expense
of some more code.

i18n: Add mutation tests

i18n: Add new module containing a Message class ...

This Message class will be used to format localized text later.

parse: Have parse run parse_file

parse: Actually add parser code for real this time I promise

parse: Add directive parser

parse: Add conditional statement parser

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: Don't mutate self.parse_value ...

I don't quite understand why this is happening but mutmut will replace
this effectful function with 'None' and cause the loop to loop forever.

parse: Add newline to make printing ParseContexts easier

parse: Add statement parsing

parse: Add code for parsing values

parse: Reserve keywords for reference names