decoupling start and shutdown

- start is no longer a blocking call
- giving it back to users
- the Stop method now waits for the timeout before closing

option.go

@@ -1,6 +1,8 @@
 package bolt
 
 import (
+	"time"
+
 	dg "github.com/bwmarrin/discordgo"
 )
 
@@ -48,3 +50,11 @@ func WithLogLevel(lvl LogLevel) Option {
 		b.logLvl = lvl
 	}
 }
+
+// WithGracePeriod gives a grace period for commands to finish prior to closing the
+// websocket connection with Discord
+func WithGracePeriod(t time.Duration) Option {
+	return func(b *Bolt) {
+		b.grace = t
+	}
+}