Updated README to reflect 404 redirection support.
Use readability to fetch article content.

Makes the whole "xpath rules" things useless. Almost any feed is now supported. CSS liferea stylesheets are also uneeded now, since readability cleans up html code a more efficient way. README was updated.
Improved caching.

No longer writes everytime a value is added, since it could cause some issues if two instances of the script were run at the same time. Now it only writes when the  Cache object is no longer in use (ie. garbage colllected).
Better detection of feeds with content provided.
Meta redirects are now supported.
Better detection of feedportal, extra url logging.