- Added object HuSourceFile, which represents a loaded / unloaded
  file into the compiler. HuSourceBuffer is now a "window" into
  a file, with the memory being mapped in.

- Adjust HuLexerMod to now keep track of the offset into a
  HuSourceBuffer. This will be the bridge between a HuSourceBuffer,
  HuToken, and HuSourceLocations.

- Next step is to get HuSourceLocations added in nicely, and
  possible adjust offset advancement now that newlines and columns
  need to be tracked.