Add mouse_xy macro

[sezanzeb]

#941

• Allows moving into both x and y directions
• Turned acceleration into a fractional value, so that x and y accelerate proportionally. For consistency, this is changed in the original mouse macro as well. After the 2.1.0 release, this shouldn't change anymore.
• The injection of mouse events was 15 - 20% too slow

[sezanzeb]

@jdoda what do you think?

[jdoda]

@jdoda what do you think?

Yeah, seems reasonable.

[sezanzeb]

Thanks. I'll merge this in a week or something, after my other pull requests.