Added `partition` and `partition_all`

Also changed generated type of `partitionby` to tuple.

See #40
oops, python 3 support
Modified docstring of `partition_all` to @mrocklin's suggestion in #65
Merge branch 'master' into HEAD

Conflicts:
	toolz/__init__.py
	toolz/compatibility.py
	toolz/itertoolz/__init__.py
	toolz/itertoolz/core.py
	toolz/itertoolz/tests/test_core.py