Make the plugins support Filebeat's pipelining

This PR fix a issue when using pipelining with filebeat.

Fixes #89

Author: ph

lib/lumberjack/beats/server.rb

@@ -381,7 +381,8 @@ def compressed_payload(&block)
       transition(:header, 2)
 
       # Parse the uncompressed payload.
-      feed(original, &block)
+      parser = self.class.new
+      parser.feed(original, &block)
     end
   end # class Parser