    paper.scale([sx, sy, ox, oy])

Scale a paper by `sx` factor in x axis and `sy` factor in y axis. `ox` and `oy` are optional and determine the origin of the scale transformation. This method effectively implements a paper zoom in/out. If the method is called a `"scale"` event is triggered on the paper. When the method is called with no parameter the current paper `scale` transformation is returned.

    paper.scale(2) // scale 2x (uniformly)
    paper.scale(2,3) // scale 2x in `x` axis 3x in `y` axis (non-uniformly)
    paper.scale(2,2,100,100) // scale with the origin of the transformation at point `x=100` and `y=100`
    paper.scale() // returns e.g. { sx: 2, sy: 2 }