Replaced --verbosity with --quiet

I wasn't using the verosity levels, but just turning logging on and off.

So I renamed the flag.

README.md

@@ -34,7 +34,7 @@ Usage
 -----
 
 ~~~
-usage: docker-gc [<flags>]
+usage: docker-gc_darwin_amd64 [<flags>]
 
 The missing docker garbage collector.
 
@@ -46,8 +46,10 @@ Flags:
                             DOCKER_GC_MAX_IMAGE_AGE)
   -s, --sweeper-time=15m    How much time between running checks to delete
                             images. (Env: DOCKER_GC_SWEEPER_TIME)
-  -v, --verbosity=1         How much logging to stderr. 0 = none. 9 = maximal
-                            (Env: DOCKER_GC_VERBOSITY)
+  -d, --dangle-safe-duration=30m
+                            How old should a dangle image be before deletion.
+                            (Env: DOCKER_GC_DANGLE_SAFE_DURATION)
+  -q, --quiet               Don't show any output. (Env: DOCKER_GC_QUIET)
 ~~~
 
 It uses the normal Docker environment variables, so if `docker info` works,

config/config.go

@@ -14,7 +14,7 @@ type Config struct {
 	MaxAgeOfImages     time.Duration
 	SweeperTime        time.Duration
 	DangleSafeDuration time.Duration
-	Verbosity          uint8
+	Quiet              bool
 	Version            string
 }
 
@@ -30,15 +30,15 @@ func NewConfig() Config {
 	kingpin.Flag("max-image-age", "How old to allow images to be before deletion. (Env: DOCKER_GC_MAX_IMAGE_AGE)").Short('m').Default("168h").OverrideDefaultFromEnvar("DOCKER_GC_MAX_IMAGE_AGE").DurationVar(&config.MaxAgeOfImages)
 	kingpin.Flag("sweeper-time", "How much time between running checks to delete images. (Env: DOCKER_GC_SWEEPER_TIME)").Short('s').Default("15m").OverrideDefaultFromEnvar("DOCKER_GC_SWEEPER_TIME").DurationVar(&config.SweeperTime)
 	kingpin.Flag("dangle-safe-duration", "How old should a dangle image be before deletion. (Env: DOCKER_GC_DANGLE_SAFE_DURATION)").Short('d').Default("30m").OverrideDefaultFromEnvar("DOCKER_GC_DANGLE_SAFE_DURATION").DurationVar(&config.DangleSafeDuration)
-	kingpin.Flag("verbosity", "How much logging to stderr. 0 = none. 9 = maximal (Env: DOCKER_GC_VERBOSITY)").Short('v').Default("1").OverrideDefaultFromEnvar("DOCKER_GC_VERBOSITY").Uint8Var(&config.Verbosity)
+	kingpin.Flag("quiet", "Don't show any output. (Env: DOCKER_GC_QUIET)").Short('q').Default("false").OverrideDefaultFromEnvar("DOCKER_GC_QUIET").BoolVar(&config.Quiet)
 
 	kingpin.Parse()
 
 	if config.SweeperTime < (4 * time.Second) {
 		kingpin.Fatalf("You must set the sweeper-time to greater or equal than 4s")
 	}
 
-	if config.Verbosity == 0 {
+	if config.Quiet {
 		log.SetOutput(ioutil.Discard)
 	}
 	return config