Add support for right-clicking

[qguv]

The pure X11 (Linux) equivalent to cliclick, called xdotool, allows the user to specify which mouse button is used when sending a click event.

[BlueM]

Right-clicking is possible by using the traditional “click with Ctrl key pressed” approach: cliclick kd:ctrl c:. ku:ctrl

However, this might not be too obvious. (And there might be peculiar target applications where right-clicking is not the same as Ctrl-clicking.) I’ll see if it can be implemented directly. Probably it’s not a big deal.

[muellermartin]

I've added a new handler in PR #42 - maybe you guys want to check this out ;)