Cleanup

This pull request includes a bunch of cleanup that I have done for CodeSkulptor.  Some notable changes:

- Fix the hash table implementation for dictionaries.
- Add dictionary pop and set discard.
- Improve/add type checking in various places.
- Fix bases for int().
- Fix newlines in regular expressions in re module.
- Use the indices function of slice instead of repeating code (incorrectly) when it is needed.  And check types correctly in indices.
- Add support for __nonzero__ and __len__ in misceval.isTrue.
- Clean up map/filter/reduce (may be somewhat redundant with other changes).