Add support for Slack

Added a new chat service and fixed some minor leftovers from the transition to string room ids.

Build notifications in slack:
![screen shot 2014-05-11 at 15 19 27](https://cloud.githubusercontent.com/assets/175675/3636035/73c84124-0f9b-11e4-8153-bc4a2f42458b.png)


Erm, this will do shitty things to any nums that are passed in. This would have to be part of a MAJOR release due to this incompatibility.

```ruby
>> 0.empty?
NoMethodError: undefined method `empty?' for 0:Fixnum
	from (irb):1
	from /Users/parker/.rbenv/versions/2.1.1/bin/irb:11:in `<main>'
>> 10.empty?
NoMethodError: undefined method `empty?' for 10:Fixnum
	from (irb):2
	from /Users/parker/.rbenv/versions/2.1.1/bin/irb:11:in `<main>'
```