images: fix markdown documentation

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)
filter flag: split out for separate --filter flags

adding tests and allowing for easy passing of filters.Args from client
to server.

Docker-DCO-1.1-Signed-off-by: Vincent Batts <vbatts@redhat.com> (github: vbatts)