gitdesc.sh assumes tag will have format v#.### and will return
major version, minor version, and micro version depending on
command.
gitdesc.sh will also add tag revision and HEAD commit if tag is
not equal to HEAD. So lrzip version may appear as
`#.###' or
`#.###-R-#######'
where `R' is count of commits since last tag.
usage
gitdesc.sh command [-r]
where command is one of:
all - entire git describe
commit - commit, omitting v
tagrev - tag revision count
major - major release version
ninor - minor release version
micro - micro release version + [tag release count-HEAD commit]
version - M.mic
-r -- get release tag only
