Adding consul v0.2.0

Hashicorp's [consul](https://github.com/hashicorp/consul) is distributed as a binary compiled golang project, much like their other project: [serf](https://github.com/hashicorp/serf) 

So this cask is very similar to [serf.rb](https://github.com/caskroom/homebrew-cask/blob/master/Casks/serf.rb)