Support Entity Metadata framework

Problem

Currently, we cannot use the very handy entity_metadata_wrapper with a field provided by video_embed_field.
It leads to an error message : "Unknown data property [field name]."

Steps to reproduce

1. create a content type called "test"
2. add it a video_embed_field field called "field_video"
3. execute the following code
   

   $node = new stdClass();
   $node->type = 'test';
   $wrapper = entity_metadata_wrapper('node', $node);
   $wrapper->field_video->set(array('url' => 'http://youtu.be/9bZkp7q19f0'));
   $wrapper->save();
   

Proposed solution

Add a property callback in hook_field_info to set the field type's property type.
Note : avoid to add a dependency on the entity API module.

(Patch coming)