make ADC use function instead of ALU entity to avoid latch problem.
tweak fastio state management.
change type of ALU operands to unsigned()
replace ALU component with functions to avoid latch delays
fix spelling error in M_immediate inherited from 6502 instruction
set documentation used to auto-generate tables
fix immediate mode operand fetching.
fix some bugs in alu_op_add().
fix fetching of opcode byte after immediate mode instruction.
fix bug with advancing PC between instructions.
reduce debugging output
simplify dummy reset programme.
drop clock speed to 50MHz until we optimise.