Make BRK a real instruction
Ignore unknown opcodes
Only need to do this on write
0xff is a valid address, so we need one more
Need one more, since 0xffff is a valid index
BRK actually does things

Allows more of the big 6502 test to run.
Print stack pointer, too
BRK quick halts if PC would be 0
BRK is two bytes, incr PC
Friendly named constants
Oops, restore removed
Fix carry bit set func
Shift after fetch, since <<8 on a byte == 0
Print correct address
Normal formatting
Better error detection
Record t so we can print it
Easy disable
Print some more things
Remember CPU state

This allows much faster debugging since we don't have to print anything
until there's an error.