[WIP] Organizations Teams API #331

This is going to be a work in progress for issue #331

So far I have implemented the API call for http://developer.github.com/v3/orgs/teams/#get-team 
What are your thoughts if I an exception tag for ApiValidationException on this method?

It would be raised if someone tried adding an organization as a member to the team (https://developer.github.com/v3/orgs/teams/#add-team-member)