Iteration-utilities

Several bugfixes and minor optimizations.

New feature:

- ``partial``.

And numerous other changes. See changelog.

Fixed various Bugs and small changes.

There are two new classes included:

- starfilter
- packed

- Fixed segmentation fault in `nth` when `retpred=True`.

- added remove parameter to `clamp`.
- made `deepflatten` string-aware. For other recusive-iterable classes a RecursionException is raised instead of freezing.