Feature/fix 11 streaming request

Fix for #11

Allows the configuration of cache path in order to be available for the invoker to clean it after use when doing streaming requests.

cc/ @koke  
If you add `NS_DESIGNATED_INITIALIZER` the other initializers will need it too:

![screen shot 2014-11-03 at 16 07 51](https://cloud.githubusercontent.com/assets/8739/4884384/4a9833da-636b-11e4-8389-48a295481438.png)