Add invoke()
Add for_each()
Add for_each_right()
Fixed typo
Python 3 compat
Fix dict callback for _iter_callback()
Rewrite for_each() and for_each_right()
Fix tests to include callback args
PEP8
Fix typo
Missing test
Merge pull request #13 from nathancahill/functions

Add invoke(), for_each() and for_each_right()