+ Document FreeBSD booting process.

+ Improve PnP compatible ROM header. Test more.

+ Some cards (e.g. 3c509) need a hard reset after being used by OS;
maybe should do a reset when etherboot starts.

+ Code improvement in many places to reduce size. Structure assignment
instead of many field assignment statements.

+ Is back to back PIO a good idea? Maybe should use versions with delay?
In fact do some drivers require slower IO access to avoid hangs?