Semaphore client.

This adds support for [Semaphore](https://semaphoreapp.com).

Getting the integration specs to pass (with vcr) was a little cumbersome.  I had to let vcr do its thing, then go in and edit the episodes by hand (removing sensitive data - api_token, etc).  I couldn't think of a better way to do this.

Let me know if you have any suggestions.