Add usage-example-template.ly
cross-voice: Remove old file
fried-headers (old): add comment

Are these booktitlemarkups really to be kept?
snippet-template: include oll-base.ily
snippet-template: fix header field naming
dev-mode: Add color -tweak
move lyrics-shorthands WIP

I leave this for now as I'm completely confused about the
behaviour of the shorthands with different LilyPond versions.
tweak-shorthands: Move file, WIP

Only started to clean up the commands and to write examples.