ENH: Add grouping utilities
Grouping sort method
check_index sanity
ENH: Reindex Grouping method
minor Grouping bug
STY: PEP-8 cleanup
ENH: Use existing helper functions.
BUG: Preserve shape of input.
DOC: Add some documentation to Groupings methods
BUG: Fix import.
ENH: Use properties for dummies.
BUG: Make sure sorting is done properly. Needs tests.
BUG: Fix group_demeans thinko
ENH: New-style class
REF: Refactor grouping class
TST: Test grouping class
COMPAT: Fix for older versions of pandas.
Merge pull request #1421 from jseabold/grouputils

ENH: Add grouping utilities code