Allow aliasing interface name (#110)

Implementation based on #57.

main.go

@@ -30,6 +30,8 @@ func main() {
 	flag.Usage = func() {
 		fmt.Println(`moq [flags] destination interface [interface2 [interface3 [...]]]`)
 		flag.PrintDefaults()
+		fmt.Println(`Specifying an alias for the mock is also supported with the format 'interface:alias'`)
+		fmt.Println(`Ex: moq -pkg different . MyInterface:MyMock`)
 	}
 	flag.Parse()
 	args := flag.Args()