Have added webhook notifications to seyren, allows http posts of json payload to be sent to a given url as a subscription target as mentioned in #131, did this a couple months ago but was sidetracked on other things, but is really useful - as is taking images of graphites graphs when the alert happens so i've kept this in, but happy if its moved to its own place as im sure the other notification types could benefit from having it as well (i use it in hipchat notifications myself as well).