Fix aggregate method doc refs
Add GroupedTable groups iterator
Refactor initial groups implementation into BaseGroups objects
More refactor progress to put everything into groups attr
Move groups tests into seperate module
Put in workaround for issue #1471
Add __repr__ for TableGroups and ColumnGroups
Add column group_by
Change test_groups to use plain functions not class
Add tests of copying and slicing grouped tables
Support item slicing and mutable operations on grouped tables
Fix bug trying to delete nonexistent _groups attr
Support copying table groups in Table.copy()
Make copying a grouped column pass tests
Add tests of grouped item access
Move keys and group_keys from BaseGroups into TableGroups
Add tests of group keys() and values()
Update sphinx docs
Inhert column name attr from original when creating new column
Add docs on manipulating groups