Make Make_Screencast.bsh truly executable

It was already marked as executable, but there was no shebang line,
therefore it would not execute properly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Refactor Make_Screencast.bsh

We now separate properly between UI and logic.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make_Screencast (cmd-line): allow specifying a region

When making a screencast, we can now confine what is recorded to a
sub-rectangle of the complete screen.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make_Screencast (cmd-line): allow specifying the frames per second

While at it, fix it on Windows (--dshow-fps).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make_Screencast (cmd-line): allow overwriting existing files

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'screencast'

Some refactorings and enhancements to the screencast script, to allow
for advanced command-line usage.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>