Allow push of a single tag

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Update docs. Make PULL up to date, remove deprecated falg and update PUSH

Docker-DCO-1.1-Signed-off-by: Guillaume J. Charmes <guillaume@charmes.net> (github: creack)
Merge pull request #4948 from creack/push_single_tag

Allow push of a single tag