Configurations per resource or per uploader

[johnkoht]

I think we should extend the configuration to enable per resource or per uploader customization. When you set the initializer, it really only address one type of resource. What if I have a project and user model and they have drastically different carrierwave versions. Rather than having to default to projects and inline my user model, we should allow the gem to pull global configs on a per resource basis.

*Option 1: Class Method
We can allow users to define the configuration in the model as a class method, i..e:

class User < ActiveRecord::Base
  def self.responsive_sizes
    { mobile: :avatar_mobile, tablet: :avatar_tablet, desktop: :avatar_desktop }
  end
end

We can probably even make this a method called in the model:

class User < ActiveRecord::Base
  responsive_images sizes: { mobile: :avatar_mobile, tablet: :avatar_tablet, desktop: :avatar_desktop }
end

Option 2: Custom Object
We can create a custom object for sizes, ResponsiveImages::Config that can define the default config. Custom configs could inherit from the default and define the customizations:

class ResponsiveImages::Config
  def self.default
    :default
  end

  def self.sizes
    { 
      mobile: :mobile, 
      tablet: :tablet, 
      desktop: :desktop
    }
  end
end

Any calls to responsive_image_tag or responsive_background_image would use the default config. You would create custom configs by inheriting from the default config:

class ProjectResponsiveImages < ResponsiveImages::Config
  def self.default
    :banner
  end

  def self.sizes
    { 
      mobile: :project_mobile, 
      tablet: :project_tablet, 
      desktop: :project_desktop
    }
  end
end

To use the custom config, you would pass it as an argument to the helper method, i.e.:

responsive_image_tag @project.image, config: ProjectResponsiveImages

Let me know if there are any other, or better, options.