Extra raw lexer tests, also test state.
More state tests.
Remove check for unused token name.
Raise assertion error on unknown token name.
Fix lexer bugs.
Further tests.
Test that invalid error code raises the right exception.
Test for catching invalid tokens.
Also check that invalid states raise an assertion error.
Remove pointless check.
Merge pull request #22 from mcmtroffaes/feature/latex_lexer_coverage

Improve LaTeX lexer coverage and some small bug fixes.