[Simh] CDC1700 simulator update

[John Forecast]

I’ve updated the CDC1700 simulator to include:

	1. Support for the 1752 Drum controller with capacities from 192KB to 3MB

	2. Implement the ability to share subroutines between interrupt service routines at different priorities.

	3. Implement a number of Simh expect scripts for customizing MSOS 5. 

		Back in the day, CDC would have supplied each site with 2 distribution tapes/card decks:

			1. A generic distribution with drivers for every supported device/feature.

			2. A distribution tailored explicitly to the customer’s configuration.

		Unfortunately, none of the generic distributions seemed to have survived but we can use the tailored distribution as the base
		for limited customization. We can easily remove support for specific peripherals but adding a new device requires finding a
		suitable update kit (there are a few available on bitsavers) and performing the update by trial and error. The MSOS 4
		customization guide (available on bitsavers) can be helpful.

This is probably the last release which will only support the 1700-series. CDC moved on to the Cyber-18 series which included an
enhanced instruction set along with the ability to address up to 512KB. The current simulator can disassemble the enhanced instruction set
(if SET CPU INSTR=ENHANCED command is used) but cannot execute these instructions.