plaintext-de: Move includes to dedicated package
plaintext-de: Add document with score examples
plaintext-de: Add (private) link to score examples

This will link to a private directory, so the .tex file won't be usable by anyone else.

The music is partially copyrighted so that wouldn't work anyway.
plaintext score examples: Small touches
plaintext-de: Update score examples

Add Schoenberg comparison Finale - LilyPond
Merge branch 'score-examples'