Fix #819: Improve docs about ID/name to names/titles mapping
Fix instances of list(six.iterkeys(d))
Merge pull request #1893 from mdboom/misc/simplify-six

Fix some six changes
Merge pull request #819 from mdboom/vo/name-mapping-docs

Clarify docs on VOTable "name" and "id" vs. numpy "name" and "title"
Add Table pickling
Add tests of table and column pickling
Add __setstate__ and __reduce__ methods so Columns can pickle
Update CHANGES.rst