DOC: add link to tips data set in rplot docs
closes #3799.

oh darn also the `'totbill'` is not a column anymore
 @jreback ok to merge?
 i wonder why the doc build was not catching this...
 hmmm.....we can include that file in the static sources (or is right?)
 ok now i'm getting a key error i think there are disparate versions of tips.csv...let me investigate...
 yep they are different, i'm going to put the one that i've linked to here, which is the one wes links to on his blog
 @jreback going to merge if u have no issues here.
 @jreback actually can u merge this and the ipython cache fix if there are no issues, i have to run out. thx!
 thanks again
