ENH: Using built-in round on a series #11763
closes #11763 

This contains changes to support `round()` (works in Python 3 only) for DataFrame, Series and Panel. Also includes `Panel.round()`.  Note on code changes - moved code from test_format.py to test_frame.py because it made more logical sense to put the testing code for `round()` into test_frame.py

small docs changes. pls squash. ping when green.
 @jreback It's squashed now.  Not sure what to do next to force the Travis CI thing to happen since it says there are conflicts
 you need to rebase on master as well 
 @jreback I think this is good to go.
 couple of trivial changes. ping when pushed (as its already green)
 @jreback pushed those changes (and squashed them as well)
 @jreback last build failed due to a URL issue.  Not sure how to restart the run
 @Dr-Irv no worries. thanks for this!

yeh travis fails once in a while on the build step. 
