UI improvements, plain ALSA audio

I had neglected to create a release for some time, this one covers quite a lot from the previous.

New keys:
c - view vertical scrolling note chart thing
v - show volume bars
enter - go to a specific track

Now outputs audio with plain ALSA, which integrates pretty nicely with the main poll() loop and doesn't need threads. (The less complexity the better!)

Volume is persisted in the new $XDG_CONFIG_DIR/minigbsrc config file.