Moved resource config values into config property to allow inherited resources to change values

Fixes #59

@glebm Can you try out this change and see how it works for you with CoffeeScript?  To solve the problem of what constructor to use I just added a new <code>resourceConstructor</code> config setting.  I wrote a test with the generated JS from the following CS code and it seems to be working.  I couldn't come up with a way of exposing a base class that didn't require calling the factory but I think this new version is definitely more flexible with setting config options after the fact.

````coffeescript
class Book extends railsResourceFactory()
  @config.url = '/books'
  @config.name = 'book'
  @config.resourceConstructor = Book

  constructor: ->
    @subclass = true    
````