Handle suspending execution when receiving SIGTSTP signal (CTRL+Z)

[timjk]

This would improve presentations by being able to pause execution, do something in the terminal, and then resume execution at the same location the presentation was at previously.

Currently I either shift between two terminals or, kill the process and start it over again - navigating to where I was in the presentation.

[mfontanini]

This makes sense. I'll see how to implement this, I guess presenterm SIGTSTP'ing itself should work.