Reading /mnt/acme/log reports a log of window create, put, and delete events, as they happen. It blocks until the next event is available. Example log output: 8 new /Users/rsc/foo.go 8 put /Users/rsc/foo.go 8 del /Users/rsc/foo.go This lets acme-aware programs react to file writes, for example compiling code, running a test, or updating an import block. TBR=r R=r https://codereview.appspot.com/89560044

Move libfmt, libutf into subdirectories of lib9. Add poll-based socket i/o to libthread, so that we can avoid using multiple procs when possible, thus removing dependence on crappy pthreads implementations. Convert samterm, acme to the single-proc libthread. Bring libcomplete, acme up-to-date w.r.t. Plan 9 distribution.

Until I hear otherwise, Refs aren't used enough to merit their own assembly. They are now implemented with locks.

Also add acme!