Previously folder hierarchies were created based on the input URL
which could result in very deep folder structures. Using SHA1 file
names also allows to check for old files more effectively (via
fileatime)
This allows to specify the cache duration for a specific
url without the need to delete the cache file first.
Instead the cache file is automatically deleted if the
duration elapsed.
The files have grown to a size where it is necessary to search
for a class in a file. This commit splits the content into one
file per class. RSS-Bridge will require implementations and
the implementations will require (once) the interfaces.
