PDP11: report RK05 drive presence more reasonably.  Add historical information in RK help.
PDP11: Updating doc for RS03/RS04 and RHC from Bob Supnik
SCP: Add comments describing the various REG initialization macros.
SCP: Add timer logic description comments to sim_timer
PDP11/VAX: Use unique drive serial numbers when writing BAD144 bad block info to newly created disk images
PDP11/VAX: Use semi-unique drive serial numbers when writing BAD144 bad block info to newly created disk images

The 32 bit drive serial number is determined by hashing the newly create filename.
PDP11: Added help to KE, KG, RF, TA, TC and TM devices.  Fixed DECtape documentation.
PDP11/VAX: Make sure that semi-unique drive serial numbers have a zero msb to avoid issues in some operating systems.
Merge remote-tracking branch 'simh/master'