CMUCL 20b tagged

 CMUCL 20b has been tagged (RELEASE_20b).  Although there have been some
changes from 20b-pre2, they've been fairly small.  I don't want to go
through another pre-test cycle.

Binaries will be uploaded soon and the webpages will be updated with the
new information.  The formal announcement will come soon too.

Also, 20b will be the last release that provides both unicode and
non-unicode builds.  I'm tired of doing the non-unicode builds
especially since I never use them.  The next snapshot might have them,
but I'm going to stop building them after that.

Ray