starting again with basic math
PLY lexer and basic parser now playing together, at least for x + y
added operators: sub, mul, div
added unary operators, + and -, and pow operator, **
now building parse trees for basic operations
added SymbolBase class, symbol function, created basic symbols using symbol function, changed lexer categories to base categories, changed tokenize to filter for lexer categories and do symbol_dict lookups
everything working in effbot up to Python expressions. Yay
Merge pull request #2 from joyjding/symbolfactory

Symbolfactory