- Less overhead.
- Switching implementations without makefile changes.
- Compatibility with specific declaration needs. (I.e. the cc65 module loader expects the read() function to be defined as fastcall but that contradicts the cfs API declaration.)
This change means that one needs to select _ONE_ cfs implementation at Contiki library link time. But this doesn't appear to be an issue as all platforms have their "favorite" implementation anyway.
