curry functions in toolz/__init__.py

TODO: arrange this better - __init__ should not have logic
TODO: test
move frequencies from recipes

Also give more performant solution
countby depends on frequencies, not groupby
use imap in countby
Merge pull request #17 from mrocklin/frequencies-performance

Frequencies performance
add curried namespace
replace comprehension with dict((...) ...)
PEP-8
Merge pull request #4 from eigenhombre/curried

PEP-8
add results to curried docstring
whitespace
Merge pull request #15 from mrocklin/curried

curried namespace
add reduceby
refine refine-by docstring
skip doctest that prints a dict
Merge pull request #5 from mrocklin/reduce-by

add reduceby