Rename and fix the function that computes the ray-line intersection

The ray was considered as a line... Now it's a real ray-segment
intersection.
Interactive lines example does not have to rely on webgl.
The ray is now used as a ray instead as a line.
Merge remote-tracking branch 'stephomi/dev-ray' into dev
Improved interactive lines example.
Removed unneded context.closePath() call.
Made Projector's painterSort stable.
Updated builds.