A factory and a test case to create RSSRead objects that read feeds off line (from a string containing the XML info)

This pull includes:

Factory class added to create RSSreader instances that read from a String instead of a real RSS feed. This class is for fast testing purpose.

New test case added to show how to use this factory.

A little refactor has been done in RSSReader::load for avoiding duplicate code.


Signed-off-by: JavierJ <javierj@us.es>