Is your feature request related to a problem? Please describe.
Very often we want to make a precise screenshot (eg, an image or a table on a webpage), but it's pretty hard to make a pixel-perfect area just via mouse.

Describe the solution you'd like
To simplify this tough task will be good to implement an ability to move the cursor by keyboard arrow keys by 1 pixel. Before the mouse press - the starting area position, when the mouse pressed - the ending area position.

Is it hard to implement?