Passing string to page for conditional compiling.

Maybe if someone know better way to make conditional compiling, please let me know.
In this commit we just take last folder in output array to distinguish purpose of compiling.
Oh. shit. I forgot, then we need to pass haml_options to different outputs too. But anyway i just want to hear feedback on this idea.

Setting
```
  guard 'haml', :output => ['test', 'public'], :input => 'app/views', :run_at_start => true, :environment_folder => true do
    watch %r{^app/views/.+(\.haml)$}
  end
```
Input file
```
      - if env=="test"
        %p testing string
      - else
        %p some other string
```
first output file at test/index.html
```
      <p>testing string</p>
```
second output file at public/index.html
```
      <p>some other string</p>
```