Merge pull request #3797 from jreback/GH3795

BUG: (GH3795) better error messages for invalid dtype specifications in read_csv
DOC: fix groupby.rst building
ENH: pull pandasjson back into pandas
DOC: add ultrajson license
TST: json manip test script. and trigger travis
BLD: fix setup.py to work on current pandas
CLN: revised json support to use the to_json/read_json in pandas.io.json

DOC: docs in io.rst/whatsnew/release notes/api

TST: cleaned up cruft in test_series/test_frame
DOC: io.rst doc updates