initial version
clean up some docstrings
simplify DominateState ctor, moving special case code to _postfix_to_nfa
remove NodeState class, use DepNodeMatch objects directly in _postfix_to_nfa's nfa_stack
add lots of docstrings
add new tests
replace ugly regular expression pattern parsing code with LR(1) parser
simplify DepNodeMatch by doing all construction in __init__, thanks to new regex parser (remove set and assign methods)
replace temporary implementation of DepNodeMatch.match
remove Operator class, since operators are now represented by Token objects
add next, curpos, and lastpos methods to PeekableStringIterator
add option to skip over whitespace to PeekableStringIterator
make NfaState an abstract base class
fix bugs in regular expression matching