Added example composer example with stitching, vignetting and bloom examples

Added a bloom shader. There are 2 implementations for it but i didn't manage to setup a proper runtime switch in time so here they are.
Unless in a HDR pipeline (32bits color, using float texture or compressed float),  you'll have values above 1.0 and below 0.0, and those will be lost by automatic clamping to 8bits colors.