Log Message:
There haven't been any simh releases in years, so convert this package
to take a snapshot from github. Update to 7964e2b72d9.

Changes: too many to list them all, full list of changes is available at
https://github.com/simh/simh/blob/master/README.md

Highlights:
- many new simulators
- simulator front panel API
- VAXstation video display simulation using SDL
- UDP and NAT packet transports
- scripting support