A few modifications on PR #60

--> PR  https://github.com/plotly/python-api/pull/60

This branch was created off `issue-58`

Improved warning messages
    
- for newline character convertions
- out-of-bounds annotations
- warnings now have a custom format (ref [here](http://pymotw.com/2/warnings/#formatting))
- warnings now have a consistent layout and vocabulary