add is_evaluted argument to Expression
must re evaluate expression returned from Block in case variables have changed
add test for Issue #43
cleanup setting python recursion limit
implement MathicsScanner in ply
progress
tokenize operators using reflect hack

cleanup MathicsScanner
refactor lexer
cleanup lexer
towards MathicsParser
towards MathicsParser
towards MathicsParser
cleanup of parsing rules
removed comment token
implement binary operator parsing
implement prefix and postfix operator parsing
remove get_rule form Operators (replaced with is_prefix and is_postfix
fix sequence parsing
fix slot and out parsing
cleanup MathicsScanner