Support multi-monitor

[kayhide]

Hello,

I updated the script and supported multi-monitor.

Using xrandr command, it lists active monitors and processes on every subsection corresponding to the monitor's position and size.

On my dual monitor environment, it works as:

$ xrandr --listmonitors
Monitors: 2
 0: +*eDP-1 2560/344x1440/194+0+0  eDP-1
 1: +DP-3 1920/476x1080/267+2560+0  DP-3

[AladW]

Closing this in favor of #155, which seems less complex (no threads) and thus easier to review.

[kayhide]

@AladW Hi, thanks for your consideration.
Okay I respect your decision.

I think I will go with my fork because in my environment, it takes more than 10 seconds if it's not parallelized and I don't want to make it that slow.
Besides, I have some other ideas to make it even faster while breaking backward compatibility.

Anyway, thanks for your great work!

[AladW]

Ideally the underlying issue on slowness would be solved, rather than pave over it with multiple threads. The only reliable solution I've found so far is ffmpeg. #146 may have some ideas, but a simple implementation (read: reviewable) implementation is preferable.