ENH: add OrderedDefaultdict to util.compat
TST: Panel ctor and from_dict should respect ordering when given OrderedDict GH3303
BUG: Panel ctor and from_dict should respect ordering when given OrderedDict GH3303
DOC: update RELEASE.rst
Merge pull request #3304 from y-p/panel_od

PR: Panel and Panel.from_dict() don't honor ordering when passed OrderedDict