Async appender support

[neuromantik33]

Hello,

I wanted to implement logback's async appender with unilog but not supported out of the box I found it tricky and had to copy a bunch of code. Can you perhaps support this feature in the future?

(def ^LoggerContext context (LoggerFactory/getILoggerFactory))
(defmethod u/build-appender :async
  [{:keys [name
           delegates
           queue-size
           discarding-threshold
           include-caller-data
           max-flush-time
           never-block]
    :or   {name                 "async"
           queue-size           256
           discarding-threshold -1
           include-caller-data  false
           max-flush-time       1000
           never-block          false}
    :as   config}]
  (let [aa (doto (AsyncAppender.)
             (.setName name)
             (.setContext context)
             (.setQueueSize queue-size)
             (.setDiscardingThreshold discarding-threshold)
             (.setIncludeCallerData include-caller-data)
             (.setMaxFlushTime max-flush-time)
             (.setNeverBlock never-block))]
       (doseq [{:keys [^OutputStreamAppender appender
                    ^Encoder encoder]}
            (->> delegates (map u/build-appender) (map u/build-encoder))]
      (when encoder
        (.setContext encoder context)
        (.start encoder)
        (.setEncoder appender encoder))
      (u/start-appender! appender context)
      (.addAppender aa appender))
    (-> config
        (assoc :appender aa)
        (dissoc :delegates))))

And the schema looks like this

{:appender  :async
 :delegates [{:appender :console
              :encoder  :pattern
              :pattern  "%p [%d] - %c - %m%n"}]}