Merge pull request #234 from emqtt/dev

Fix issue #233 - emqttd plugin cannot include_lib("emqttd/include/emqttd.hrl")

.gitignore

@@ -6,6 +6,7 @@ deps
 *.plt
 erl_crash.dump
 ebin
+!ebin/.placeholder
 rel/emqttd
 rel/emqttd*
 .concrete/DEV_MODE

ebin/.placeholder

@@ -0,0 +1 @@
+emqttd plugin cannot include "emqttd/include/emqttd.hrl" without this directory:(