Micro-optimize _tokenize()
Micro-optimize _tokenize()

 - A small modification to _initial_token_re_match makes it reject
   comments too, saving some manual code (and probably lots of string
   copying).

 - Reorganize things to handle 'previous' in a nicer way.

 - Use tuples instead instead of lists in the no-tokens and _T_HELP
   cases. Could preallocate and return an empty _Feed too, but it seems
   like overkilling it.

Profiling done with cProfile and line_profiler.

ulfalizer/Kconfiglib,ulfalizer/Kconfiglib