Reorganize sources and adjust Makefile accordingly.
Clean up style.
Add unit testing stub.
Add comment tests.
Test single-character token. Fix input reading.
Test all single-character tokens.
Remove ',' and ':' from operator characters.
Test whitespace.
Test literals, identifiers, and operators.
Add file position to failed unit test output.
Test adjacent identifiers and string literals.
Test adjacent integers and identifiers.