[cmsMake] support multiple generators

[wil93]

This is purely a feature request.

I propose that, if some gen/GEN line starts with ./ then it will be treated as a whole command and not just generator arguments.

This does not break old gen/GENs (as long as they didn't require some weird things that start with ./) but allows us to write modern gen/GENs which can use multiple generators like this:

#ST: 5
#COPY: testo/example0.txt
#COPY: testo/example1.txt

./gen/random.py 10 15 16
./gen/hard.py 10
...

Now that I think about it, to be even more backwards-compatible, we could introduce a #RUN: <command> instruction.

[wil93]

Update: #RUN: <cmd> may be better, because sometimes you just want to use echo 1 2 3 as a generation command.