[WIP] Add Deployments API support

## Add support for deployments API

This pull request includes the following functions:
- Support for preview APIs at the client level
- List/Create Deployments
- List/Create Deployment Statuses
Go convention is to use [mixed caps rather than underscores](http://golang.org/doc/effective_go.html#mixed-caps).  That said, I'd probably just shorten `deployment_req` to `deployment`.