Integrate asset manager - Piler

Hi!

This is again not a proper pull request and I don't expect it to be directly merged. Tests are not updated etc.

But anyway I integrated [Piler](http://epeli.github.com/piler/) with Zappa and I think it fits in very well as originally expected since many of the features in *node-pile* are originally inspired by Zappa :)

This would close issues #19, #79 and #94.


This changes the API for @client, @shared, @css and @stylus. 

The API is now 

    @client mynamespace: -> alert "hello"

If you omit the namespace it will default to global namespace in *node-pile*

Script and style tags are rendered with *renderStyleTags* and *renderScriptTags* helpers. The global namespace is always rendered and others can be added as arguments.  See [this example](https://github.com/epeli/zappa/blob/pile-integration/examples/assets.coffee)


There are some issues when serving build-in assets and I think this should be rethought if we really integrate this. *[@enable 'server jquery'](https://github.com/epeli/zappa/blob/7969d36b35a3829282dd8edfd5f77ae4e49bbbd4/src/zappa.coffee#L124) style* does not work so nicely with this. I have been thinking of adding support for ender-js for *node-pile* which could resolve this issue nicely.