Major refactor in Model, check details.

  - Added documentation for most methods.
  - Added the fetchCollections method.
  - Refactored how the toJSON method works a bit, it doesn't get defined
    if ActiveRecord support is not declared inside Sharkbone.Config
  - The createDotSyntaxCollectionGetters method is defined and called
    upon initialization if Backbone.RelationalModel is present, this
    enables the dot syntax to fetch hasMany collections in a model.