ENH: Fullscreen

Closes #387.

I have only changed one example (`text_visual.py`), assuming people are happy with the other changes, I'll change all the other examples.
Now we don't explicitly close the FT_Library. However, this would normally be called when the application exits, so although it's not clean, it's hopefully not necessary. We have been getting some random segfaults at the end of the `nobackend` tests on Py3k, and I think it's due to this.