Ignore keystrokes that are not exactly Command+Shift

[foxel]

Hi. First of all, this isan awesome project.

My issue is that when I use combinations like Command+Shift+F I end up with switched layout. I see this can be fixes by combining "switch after release" with checking that no other buttons were pressed while the shift was pressed.

I could do a PR for that, but I couldn't find the build instructions for the project.