Compiler warnings addressed
types.StructSequence: coming along, checkpoint
StructSequence -> NamedTuple

At first, the implementation was based more upon structseq.c,
but this shifted as I fleshed it out, eventually working
the slots precisely like a tuple.

This will probably be moved into collections as a result.
... and b.types.NamedTuple -> b.collections.NamedTuple
NamedTupleMeta.__getitem__ implemented
NamedTupleMeta.__iter__ implemented
Unused variable
NamedTuple.__repr__ implemented
NamedTupleMeta.__new__: remove some finicky bases checking which does not matter now that NamedTuple is a real class (and not a template)
NamedTuple.__new__ *args/**kwargs permutations implemented
Consistent, fully-qualified tp_names
Move Memoizer into types.c