preliminary implementation of interrupt forwarding
connected interrupt pin

fixed shorted halt pin
leave interrupts disabled until enabled by Z80 code

added a warning regarding the shortend halt pin
added generic interrupt forwarding method

not sure if Z80 gets correct interrupt id as of now

needs further investigation
confirmed interrupt forwarder to work

implemented interrupt vector map in Z80 crt

Z80 code can now provide own ISRs

started to provide names for MMIO addresses

tested with sdcc ISRs
further improved interrupt forwarding code
minor changes before merge
Merge branch 'interrupts'