Generate lexers for programs in various languages from the DFA

[timtadh]

This is an experimental PR which contains support for generating lexers for programming languages directly from a DFA specification. It does not use the same API as the rest of lexmachine.

For a first proof of concept I wrote a super simple generator for Python. The code it produces is probably not optimal for python.

This branch may or may not every be merged. Chime in if you have a good use case or language you want support for (including Go).