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.
All decoration, particle and module interfaces now takes a
pixman_image_t parameter, and all drawing is done using pixman APIs.
The wayland/xcb backends implement a new interface functions,
get_pixman_image(), that should return a pixman image instance that is
suitable for rendering.
In the wayland backend, the image uses the same backing data as the
cairo surface.
In the XCB backend, we create a new image each time, and then blit it
to the cairo surface at commit time.
