Fifth Software Update
Here is another release of the software, adding support for the 3 serial ports and a master-only implementation of the Wire library (I'll work on slave mode in a couple weeks). Several bugs were also fixed.
Special thanks to Neil Hand for testing the Wire library and comparing waveforms to the AVR version on his logic analyzer. :-)
Non-serial USB types are still missing, but I plan to work on those over the weekend and early next week, hopefully with a release by the middle of next week.
As always, please report any bugs or incompatibilities. Detailed and reproducible bug reports are tremendously helpful. Poor ones slow me down. Please, always send the complete code you're compiling, and always copy-and-paste (or screenshot) any error messages.