open to work attribute youtube_user_name
add youtube_user_name to class SubscriptionFeedParser

This feature need for future identificate owner of user subscription. If we render field title, then can get a user name in  "display" wich can not operate with standart queries.
adding content_length option for remote videos
Fixing embed_html5 tab alignment
Allow the sandbox attribute to be set on the html5 embed
Loosening json dependency
loosen the nokogiri dependency
Add User#channel_uri.
Refactor errors.

- Add some tests to assure error raising from client is correct
- Define the current errors under the YouTubeIt namespace
Introduce ResourceNotFoundError.

- Is raised whenever the api responds with 404
- Used to raise UploadError which made no sense at all for a missing video etc
Add changelog with info about changes to error handling.
adding retrieve region and category-specific standard video feeds
Implement ActiveSupport-based Instrumentation
Fix syntax error in sample code.
Add channel_id to Comment
Update test
Add googlePlusUserId to Comment
loosen the nokogiri dependency
Adding fullscreen option for HTML5 embed

Without this option the full screen youtube option doesn't work
Merge pull request #174 from r72cccp/master

add youtube system user name to client.subscriptions query