Implemented most of the base parser.

This includes branching arguments as well as commands, eg.

    app user create <id> <first> <last>
    app user <id> delete
    app user <id> rename <to>

Of note, required/optional flags and positional arguments are not
currently enforced.

global.go

@@ -5,6 +5,6 @@ import "os"
 func Parse(cli interface{}) {
 	parser, err := New("", "", cli)
 	parser.FatalIfErrorf(err)
-	err = parser.Parse(os.Args[1:])
+	_, err = parser.Parse(os.Args[1:])
 	parser.FatalIfErrorf(err)
 }