Accept region geometry on command line

[ropery]

Hey, pretty neat idea using xinput + dzen2 to overlay keystrokes.

However, xscast currently only allows selecting a window via xwininfo. I'd like to request an option -g, for passing simple X-style geometry on the command line,

xscast -g 640x480+300+100 o.gif

You may wonder how that would ever be useful.
Well, with FFcast it can be very useful. The following will record a free selection (drag the mouse):

ffcast -s xscast -g %g o.gif

A side effect of this is that the user no longer has the window frame to indicate the recording area.
This is easy to fix by passing -f x11grab -show_region 1 to ffmpeg.

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An unrelated side note:
Try adding -layers Optimize before $outfile in the convert command.
It can seriously reduce the file size.