Compile options support

@mwylde Hey Micah, here's what I was thinking with regards to compiler options support.  This way, in `slinky.yaml`, we can say:

```
compile_options:
    scss:
        dev:
            :debug_info: true
        prod:
            :debug_info: false
    haml:
        ....
        .....
```

Let me know what you think! 
I think this is actually the issue. We're requiring version 3.1.x of the haml gem, but you've updated the gemfile to install 4.0.