ENH: Styler.to_latex()
I have created a [branch](https://github.com/toobaz/pandas/tree/style_to_latex) adding a ``to_latex`` method to ``Styler``.

It is nowhere near readiness, and in particular:
- supports only cell background color as of now - adding some attributes should be trivial, adding others might be less so
- most importantly, it works on a copy of the dataframe casted ``.astype(str)``, which is plain wrong because it discards features such as float formatting. For a good result, a better integration is needed with the code that currently does cell formatting in ``DataFrame.to_latex``.

This said, if anyone feels like experimenting, it might be slightly better than starting from scratch.

One aspect which I think is useful, even aside from this branch, and might benefit some discussion, is the pair of methods ``_latex_preserve`` and ``_latex_restore``, which basically replace LaTeX commands so that they are not disturbed by escaping, and then restores them. There might be better way to code this, but I really think this is something we need to implement, and to offer to users who happen to nest LaTeX code in their cells.