Make does_styling attr public. Bump version to 1.6.

This is more often what's intended when is_a_tty is examined. While a caller could keep track of what he's passed to the Terminal constructor, it is often more convenient to have the info available directly on the instance, which we're already passing around everywhere.
Add Sphinx build dir to gitignore.
Add `fullscreen()` and `hidden_cursor()` to the auto-generated docs.
Make PEP-8-compliant.