Enable TTS_KEY_Q == TTS_KEY_A

Alters the newKeyHandler function to run either the front or back side
of a card using a single shortcut key.
Updates to README

Explains how to use the same key between the front and back of a card
and the limitations of it at this point (i.e. for cards where both the
front and back have TTS).
Merge feature/play-both

Brings in the ability to assign the same key to the fronts and backs of
cards.