String.l and it's replacement

Hi Max,

I tried the newest netzke master and I saw, that you got rid of `String.l` which is totally cool :)
But I'm a bit confused how it got replaced. For example the following works great:
```ruby
js_configure do |c|
  c.some_method = <<-JS
    function(){
      // some stuff
    }
  JS
end
```
When the component gets serialized, the `some_method` attribute won't be a String.

But as soon as there's is some nesting, it won't work and I need ```ActiveSupport::JSON::Variable```:
```ruby
js_configure do |c|
  c.listeners = ActiveSupport::OrderedOptions.new
  c.listeners.special_key = ActiveSupport::JSON::Variable.new(<<-JS)
    function(){
      // some other stuff
    }
  JS
end
```

So what's the magic behind this?
I also updated the `CHANGELOG.md`.