refactor emit() and emitwithcallback(), address comments

apid.go

diff --git a/apid.go b/apid.go
index 7da00d9..fdf937c 100644
--- a/apid.go
+++ b/apid.go
@@ -5,7 +5,7 @@
 )
 
 const (
-	SystemEventsSelector EventSelector = "system event"
+	SystemEventsSelector  EventSelector = "system event"
 	ShutdownEventSelector EventSelector = "shutdown event"
 )
 
@@ -77,11 +77,10 @@
 }
 
 func ShutdownPlugins() {
-	Events().EmitWithCallback(ShutdownEventSelector, ShutdownEvent{"apid is going to shutdown"}, ShutdownHandler)
+	Events().EmitWithCallback(ShutdownEventSelector, ShutdownEvent{"apid is going to shutdown"}, shutdownHandler)
 }
 
-
-func ShutdownHandler(event Event) {
+func shutdownHandler(event Event) {
 	log := Log()
 	log.Debugf("shutdown apid")
 	shutdownChan <- 1
@@ -91,7 +90,7 @@
  * this is used to prevent the main from exiting
  */
 func WaitPluginsShutdown() {
-	<- shutdownChan
+	<-shutdownChan
 }
 
 func AllServices() Services {

data_service.go

diff --git a/data_service.go b/data_service.go
index 62523e0..1b84328 100644
--- a/data_service.go
+++ b/data_service.go
@@ -16,7 +16,7 @@
 }
 
 type DB interface {
-	Ping() (error)
+	Ping() error
 	Prepare(query string) (*sql.Stmt, error)
 	Exec(query string, args ...interface{}) (sql.Result, error)
 	Query(query string, args ...interface{}) (*sql.Rows, error)

events_service.go

diff --git a/events_service.go b/events_service.go
index 0e249c9..1106f2d 100644
--- a/events_service.go
+++ b/events_service.go
@@ -11,8 +11,11 @@
 type EventHandlerFunc func(event Event)
 
 type EventsService interface {
-	// publish an event to the selector
-	Emit(selector EventSelector, event Event)
+	/* publish an event to the selector.
+	It will send a copy of the delivered event to the returned channel, after all listeners have responded to the event.
+	Call "Emit()" for non-blocking, "<-Emit()" for blocking.
+	*/
+	Emit(selector EventSelector, event Event) chan Event
 
 	// publish an event to the selector, call the passed handler when all listeners have responded to the event
 	EmitWithCallback(selector EventSelector, event Event, handler EventHandlerFunc)
@@ -42,13 +45,15 @@
 	Count       int
 }
 
+// use reflect.DeepEqual to compare this type
 type PluginsInitializedEvent struct {
 	Description string
+	// using slice member will make the type "PluginsInitializedEvent" uncomparable
 	Plugins []PluginData
 }
 
 type PluginData struct {
-	Name string
-	Version string
+	Name      string
+	Version   string
 	ExtraData map[string]interface{}
 }