Add initial support for sendMediaGroup.

log.go

@@ -1,13 +1,14 @@
 package tgbotapi
 
 import (
-	"os"
 	"errors"
 	stdlog "log"
+	"os"
 )
 
 var log = stdlog.New(os.Stderr, "", stdlog.LstdFlags)
 
+// SetLogger specifies the logger that the package should use.
 func SetLogger(newLog *stdlog.Logger) error {
 	if newLog == nil {
 		return errors.New("logger is nil")