title: Slack API team invitation
body: <p>I am looking for a call which could send a Slack team invitation email to a new user from my application. I searched it in the SlackAPI but I didn't find anything. Is it possible to create an application which would sent invitations on my behalf?<br>
  I'm currently using slacker as a Python wrapper, but if there is any better library which provides invitations I can start using it.</p>