CLN: refactored url accessing and filepath conversion from urls to io.common
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