~ecs/tm

ref: 95cb618f450695312ff6849e7c6e86709e985ae9 tm/tm-update-ref -rwxr-xr-x 268 bytes
update-ref: index is a normal ref now
resolve-ref: initial commit

Replaces resolve_ref in lib.sh
update-tree: create nonexistent files/directories
update-tree: initial commit
Fix handling of ambiguous ref prefixes
insert: handle trees
Rewrite in POSIX sh

Also don't compress objects and make a few other small changes to the
spec.