Decrease of default code base

Currently, the standard shipping of FeedAPI has ~ 300 K of code without simplepie. By narrowing down the standard shipping (the feedapi project) to its core modules: feedapi, feedapi_node, feedapi_node_views and parser_simplepie we could cut down to 200K.

We could put the other modules (feedapi_inherit, parser_common_syndication, feedapi_aggregator) into its own projects. Breaking out sub modules into their own projects would have several advantages:

* Allows different speeds - e. g. we could upgrade the core modules pretty quickly to D6 without causing confusion
* Gives us a better understanding of which modules are being used - keeping e. g. feedapi_aggregator in its own project creates the possibility of a community to establish around it.
* Keeps things small and simple.