Sends a message to Slack for each ticket sale on Amiando.
Needs these environment variables to run:
* SLACK_URL: something like https://xxxx.slack.com/services/hooks/incoming-webhook?token=yyyyy
* SLACK_CHANNEL: a channel name to post (like "#tickets")
Procfile is provided for easy deployment on Heroku.
You could then enter "http://xxx.herokuapp.com/amiando-server-call" in Amiando's "Integration" page.
SLACK_URL and SLACK_CHANNEL can also be added as Heroku config variables.