Add 'iter_reads' methods to 'ReadParser' class. (Same as '__iter__' method for the class.)
Change some 'ValueError' exceptions in Python wrapper to 'IOError' exceptions.
Place 'ReadParser' and 'ReadPairIterator' objects in the 'khmer:: python' namespace.
Create a common initializer for types. (Space savings in the Python wrapper sources + better Pythonic citizenry.)
Replace 'new_read_parser' factory function with 'ReadParser' class.