Major Logging Overhaul

in this commit:

- centralize logging output handler.
- set global Info/Debug/Error log levels based on config file or flags.
- remove per-plugin debug arg handling.
- add a I!, D!, or E! to every log message.
- add configuration option to specify where to send logs.

closes #1786

plugins/outputs/amqp/amqp.go

@@ -153,10 +153,10 @@ func (q *AMQP) Connect() error {
 	}
 	q.channel = channel
 	go func() {
-		log.Printf("Closing: %s", <-connection.NotifyClose(make(chan *amqp.Error)))
-		log.Printf("Trying to reconnect")
+		log.Printf("I! Closing: %s", <-connection.NotifyClose(make(chan *amqp.Error)))
+		log.Printf("I! Trying to reconnect")
 		for err := q.Connect(); err != nil; err = q.Connect() {
-			log.Println(err)
+			log.Println("E! ", err.Error())
 			time.Sleep(10 * time.Second)
 		}