More additions to mods repo

[Bill E]

Added a new ultility, drumupdater, that will read a rim/bin tape and load it to a drum track, along with a 'directory' entry. The switcher.rim program now does as shown.

Some bugfixes in DCS2, some new include files, a new m1pp feature, doc updates. A new preloaded drum image. I'm probably forgetting something.

Repo is, as always, https://github.com/wjenh/pidp1-mods.git

Bill