The IP5 usage of ld65 segments and zeropage variables was made compatible with cc65 C programs already a while ago. This commit is the next logical step which is to introduce the actual C interface to IP65.
IP65 for C programs shares the the ip65.lib / ip65_tcp.lib with IP65 for assembler programs. However the various libraries from the 'drivers' are not reused. Instead there's exactly one library for every target named ip65_<target>.lib. Those libraries contain only functions used by ip65.lib / ip65_tcp.lib.
TODOs:
- Introduce c64_timer.s and atr_timer.s.
- Add a C interface to the rest of the IP65 functionality (especially TCP).
