SCons is all working, so remove Makefile stuff.
Protocol23: Moved all protocol23-specific files under src/protocol23 (apart from SCons stuff),
in preparation for splitting this off into a separate repo.

Also changes in the following files.

SConstruct:
- Various path changes.

fop.xconf:
- FInally sorted out pulling in of fonts by relative path, largely by guesswork,
since various instructions on the Internet and in the file itself didn't help.

yaml2dracula.rb:
- Changed embedded paths in generated HTML.