Use urlparse library to check feed urls
Support for relative urls in feed
Check article length is big enough

Avoids replacing rather useful descriptions with empty string
Check url before looking for provided content

Also use lenHTML() function defined a lately
Add 'feedurl' argument to Fill

Was needed for commit f3c2c34
Make Fill return True when it had done sth useful
Improve Cache code

Removed _new flag. Slightly more stable and cleaner.
Improve options and limits

New limits are possible: time limit, max number of item fetched, and max number of item taken from cache. Fill third argument is now Fast=True, which is self-explicit. (Complexity of the changes made separate commits impossible).