add reticule

[bgstack15]

Features

• Fixes #21
• Updates how the text is selected from the dropdown, so zoom levels >10 work if the user adds them to magnus directly.

Known bugs

The reticle option can distort the entire image if the window is not squared. The 300x300 minimum is good enough. The problem does not occur if you do not use the --reticule option.

Not tested

With CSD/headerbar.

References

• https://stackoverflow.com/questions/28357155/how-to-edit-pixels-of-a-pixbuf-in-python-gdk
• https://stackoverflow.com/questions/26713547/change-the-colour-of-pixels-in-a-gdkpixbuf-gtk3

[bgstack15]

I cannot find on the Internet the old Windows program i.Look, but my inspiration for the reticule and color info was that program.