* Rename and move sbysrc/demo[123].sby to docs/examples/demos
* Make them use multiple tasks for multiple engines
* Scan docs/examples for sby files for make test
* `make ci` is now `NOSKIP` by default
* Skip scripts using `verific` w/o yosys verific support
* This does not fail even with NOSKIP set
The $stable value change expression cannot be true for a non-x signal in
the initial state. This is now correctly handled by the verific import,
so the dpmem example needs to start assuming `$stable` only after
leaving the initial state.
