no need to get x and y anymore, move getHeight/Width into private zone
moveUp/down/left/right is now done internally, so no need to expose it
to the outside world
when mouse is outside (or at the edge) of the screen, emit events that
accelerate camera movement in intended direction. Cap velocity at
certain speed.

Add new event "stop camera" when user has moved mouse within screen
again.
only emit stop event when mouse was not on screen and appeared on screen
after that
emit move camera event with a direction as a vector.
let keyboard emit correct event (so multiple keys can be held)
use same logic as in keyboard to camera with mouse around, allows
diagonal movements again.
screen is now a property of mouse
remember the last sent move vector to camera. Do not repeat emitting the
same event when the vector to be sent is the same as the last sent
vector.
boyscouting
Merge pull request #5 from stefanhendriks/fix-camera-movement-with-velocity

Fix camera movement with velocity