ENH: Conditional HTML Formatting
closes https://github.com/pydata/pandas/issues/3190
closes #4315

Not close to being done, but I wanted to put this here before the meeting. Maybe someone will have a chance to check it out.

~~http://nbviewer.ipython.org/github/TomAugspurger/pandas/blob/638bd3e361633a4c446ee02534e07b8a9332258a/style.ipynb~~

~~https://github.com/TomAugspurger/pandas/blob/stylely/style.ipynb~~

[latest example notebook](http://nbviewer.ipython.org/gist/TomAugspurger/82a53e11993469cb29a1)
