Put the appendix under CC-BY 4.0

The title says this all. I hereby relicense my contributions to the appendix under the CC-BY 4.0 license.

For this to complete, I need similar statements from all other contributors: @robbertkrebbers @jjourdan @abizjak

See merge request !16

This fact is deduced from reducibility. Unfortunately, this sometimes depends on the type of states being inhabited, so that this additional hypothesis sometimes appear.

Conflicts:
	docs/program-logic.tex