Added originAt support to Image

[danielost]

Added originAt support to Image (Issue #122)

Method works correctly and can take Vec, Point, x and y coordinates and polar coordinates just like the originAt in Picture.

Example with x, y coordinates:

val atAndOriginAt =
      Image
        .circle(100)
        .at(25, 25)
        .debug
        .beside(Image.circle(100).originAt(25, 25).debug)

Output:

I've also updated the docs.

[noelwelsh]

👍