Repo cleanup

This is another set of repository cleanups:

• remove *-dev install-time dependencies for the apt packages (still can't figure out what they were doing there)
• remove some more old tcl/tk-related build targets
• remove old "messageoddness" patches which are no longer relevant for Pd-l2ork
• start a new section in manual to document differences between Pd-l2ork and Vanilla
• remove "readmesdir"-related lines and targets-- just leave readme files in their respective libdirs

This is on the road to eventually getting rid of "doc/" by merging what is (eventually) left into "pd/doc"