Merge pull request #3808 from jreback/iocom

CLN: refactored url accessing and filepath conversion from urls to io.common
DOC: turn off the ipython cache

Also clean up some unused import there

DOC: disable ipython cache
DOC: add link to tips data set in rplot docs
DOC: replace totbill with total_bill

CLN: whoops wrong filename
DOC: make tips.csv consistent
Merge pull request #3809 from cpcloud/ipython-cache-fix

DOC: turn off the ipython cache
Merge pull request #3802 from cpcloud/tips-dataset-link

DOC: add link to tips data set in rplot docs
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
API: to_json now writes to a file by default (if None is provided it will return a StringIO object)
     read_json will read from a string-like or filebuf or url (consistent with other parsers)