Sound volume & music

[sasja-san]

The "stage success" sound is really loud compared to the game music. It would be nice if there was some slider (or config file option) to change the volumes they are set to.

A second issue is that the music loops pretty badly. It sort of cuts out after a while and starts over. It should probably

1. Just fade out when the track ends.
2. Skip to a seamless prior point in the audio file when the file end is reached.