feat(scanner): add option to use fsnotify based scan watcher (#232)

* First cut at fsnotify support. Tested on Linux.

* Fixed bug in logging.

* Fixed lint issues.

* Added new scan watcher option to README.md

* Inverted conditional and dedented following code as per PR discussion.

* Changed command line switch and error return on ExecuteWatch() as per GH comments.

* Scan watcher: Removed scan at first start. Modified watcher to set a 10 second timer and then process in bulk.

Co-authored-by: Brian Doherty <brian@hplaptop.dohertyfamily.me>

cmd/gonic/gonic.go

@@ -36,6 +36,7 @@ func main() {
 	confCachePath := set.String("cache-path", "", "path to cache")
 	confDBPath := set.String("db-path", "gonic.db", "path to database (optional)")
 	confScanInterval := set.Int("scan-interval", 0, "interval (in minutes) to automatically scan music (optional)")
+	confScanWatcher := set.Bool("scan-watcher-enabled", false, "whether to watch file system for new music and rescan (optional)")
 	confJukeboxEnabled := set.Bool("jukebox-enabled", false, "whether the subsonic jukebox api should be enabled (optional)")
 	confProxyPrefix := set.String("proxy-prefix", "", "url path prefix to use if behind proxy. eg '/gonic' (optional)")
 	confGenreSplit := set.String("genre-split", "\n", "character or string to split genre tag data on (optional)")
@@ -134,6 +135,9 @@ func main() {
 		tickerDur := time.Duration(*confScanInterval) * time.Minute
 		g.Add(server.StartScanTicker(tickerDur))
 	}
+	if *confScanWatcher {
+		g.Add(server.StartScanWatcher())
+	}
 	if *confJukeboxEnabled {
 		g.Add(server.StartJukebox())
 	}