Rename README.OPL to README.Music and extend.

Chocolate Doom now has a bewildering array of different options for
music playback and it's worth documenting them properly. Extend the
existing README.OPL file to describe the other options that are
available, and rename it to README.Music as it's no longer just about
OPL playback.
Simplify INSTALL.template music notes.

Now that there is more extensive documentation in README.Music, remove
some of the details from the INSTALL files and just include a
reference to it.
Merge branch 'master' of https://github.com/chocolate-doom/chocolate-doom
Add some more code comments
Release Crispy Doom 1.1