New class XmlParser

add initial parsing of XML responses
Error handling and XML parsing

- Provider class signals errors when network reply received
- Add parsing of XML reponses to OEmbedManager
Add more support for response values to parsers
Add more url schemes and API endpoints
Delete Provider when done
Extend test for OEmbedManager class
Add thumbnail values to Response class
New class Video

Added new class Video which represents the resource type "video".
New class Rich

Added new class Rich which represents the resource type "rich"
Support for types video & rich

Added support for the resource types "video" and "rich" to
the JSON and XML parsers.
Resource types Link and Photo

Added support for the resource types "link" and "photo" to the
JSON and XML parsers.
Add render() method to all resource types
Add first usage example