Summary:
Applying the changes added for mesh rasterization to ensure that +Y is up and +X is left so that the coordinate system is right handed.

Also updated the diagram in the docs to indicate that (0,0) is in the top left hand corner.

Reviewed By: gkioxari

Differential Revision: D20394849

fbshipit-source-id: cfb7c79090eb1f55ad38b92327a74a70a8dc541e