Precise selection via keyboard

[captainbrosset]

Not sure if this is something for the spec, or just a browser implementation detail, but operating with the mouse is nice, but not precise. Once you get close to the pixel you want to pick the color from, switching to the arrow keys on the keyboard to move pixel by pixel would help a lot.

[ferllings]

This is also important for accessibility.
For people who can not use a mouse, this is important that they can move, not only at precise pixel speed, but also with much faster speed to reach the targeted screen section.

And thanks for your work, this api will be super useful.