Add podman commit command

podman commit allows the user to commit containers
as images with options of tagging th image, setting
a commit message, setting the auther, and making
changes to the instructions.

Signed-off-by: umohnani8 <umohnani@redhat.com>

Closes: #143
Approved by: rhatdan

cmd/podman/main.go

@@ -35,6 +35,7 @@ func main() {
 
 	app.Commands = []cli.Command{
 		attachCommand,
+		commitCommand,
 		createCommand,
 		diffCommand,
 		execCommand,