groupby supports non-callable key functions
reduceby supports non-callable key function
describe non-callable index in groupby docstring
rename groupby func argument to key
countby supports non-callable key function
Merge branch 'master' into support-non-callables
use non-callable arg to simplify reduceby example
Merge pull request #191 from mrocklin/support-non-callables

Support non callables in `groupby`, `reduceby`