Specify program version at build time

The version string is obtained by running `git describe` rather than
being hardcoded in `strings.go`.

Makefile

@@ -4,7 +4,7 @@ mumbledj: main.go commands.go parseconfig.go strings.go service.go youtube_dl.go
 	go get github.com/karmakaze/goop
 	rm -rf Goopfile.lock
 	goop install
-	goop go build -o mumbledj
+	goop go build -o mumbledj -ldflags '-X strings.VERSION $(shell git describe --tags --dirty)'
 
 clean:
 	rm -f mumbledj*

main.go

@@ -214,7 +214,7 @@ func main() {
 	flag.Parse()
 
         if version {
-		fmt.Printf("MumbleDJ %s\n", VERSION)
+		fmt.Printf("MumbleDJ v%s\n", VERSION)
 		os.Exit(0)
         }
 

strings.go

@@ -8,10 +8,10 @@
 package main
 
 // Current version of the bot 
-const VERSION = "v2.8.15"
+var VERSION = "Unknown"
 
 // Message shown to users when they request the version of the bot 
-const DJ_VERSION = "MumbleDJ <b>" + VERSION + "</b>"
+var DJ_VERSION = "MumbleDJ <b>v" + VERSION + "</b>"
 
 // Message shown to users when the bot has an invalid API key.
 const INVALID_API_KEY = "MumbleDJ does not have a valid %s API key."