This allows you to configure the width of each side of the border
individually. border.width can still be used, and will set all four
borders to the same width.
Closes#77
This is an integer that specifies the amount of scrolling that needs
to be accumulated before a wheel-up/down event is emitted.
A higher value means you need to drag your fingers a longer distance
before the event is emitted.
The default is 30.
