refactoring
clarify comments in the pyLRparser grammar
fix strlit bug
fix overlong line
improve stack var error messages
add test for the start condition algebra
more testing

* currently borken, as messages are reported to the wrong logger
factor out the encoding of epsilon transitions in NFAs
minor pep8ification
begin abstraction of the lexer alphabet

* use pyLRp.alphabet.Epsilon singleton instead of '' for epsilon
* add the Alphabet abstraction (to determine the iteration range
  in the DFA builder in future)
use pyLRp.alphabet abstraction

* currently the use of ByteAlphabet is hard-coded in the
  lexer generator
bugfix: use alphabet abstraction in equivalence class construction
add comments where future refactoring will be required
character filter classes for future unicode regex support
refactoring: remove useless if statements
unicode filter bugfix