Represent a face contour. A contour is a list of points on a detected face, such as the mouth.
When 'left' and 'right' are used, they are relative to the subject in the image. For example, the
is the subject's left eye, not the eye that is on the left when viewing the image.
Gets a list of 2D points for this face contour, where (0, 0) is the upper-left corner of the image. The point is guaranteed to be within the bounds of the image.