Clean up the compiler

[klange]

• [x] Make everything reentrant.
  • Will help with compiling across multiple threads.
  • Compiler should suffer no performance impact from carrying around a context object.
• [ ] Expose a better API than just the top-level krk_compile()
  • Can we expose subexpression compilation?
• [ ] Can we fix error handling to get the best of both clear early SyntaxErrors and actually detecting multiple parse errors?
  • There's a lot of places where we may not be correctly breaking out of loops on errors.
  • We need a better system for collecting errors than raising a single exception or printing.
• [ ] Merge the scanner into the compiler.
  • No solid reason for these to be separate sources, only done that way because of CI.
  • Might be able to eliminate the separation between parse rules and the big token enum?
  • Expose a better scanner API so we can build better REPL tools.

[valoeghese]

The title of this issue is extremely relatable