Remove Faraday dependency and move to depending on Yammer's Yam gem

[synth]

I figured it would be more reliable to use Yammer's Yam gem to handle the low level requests, but I liked your high level abstraction, so I made this gem depend on Yam instead of calling Faraday directly.

Definitely needs some code review though, but its working for me on my production app now...

[tiabas]

Might you like to checkout a version of the Yammer gem that I have been working on. https://github.com/tiabas/yammer-client

[synth]

@tiabas this looks similar to roadly's yammer gem, no? I still see an advantage to depending on Yammer's own yam gem so that if something like the endpoint changes, downstream dependencies will be updated right away rather than relying on third party gem's to update themselves. The api you have built looks nice though.