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.
- Adding the algorithm in pseudo code in the comment would explain the code for people not familiar with bloom.

- Links are good for explanations, but can go offline, so copy the crux of it in comments, and if possible find computer science papers on the subject like for example https://otik.uk.zcu.cz/xmlui/bitstream/handle/11025/11161/Toth.pdf?sequence=3 . Papers has scientific rigor that help defining and then using the good terms, and giving formula and reasonning behind helping in return googling for more details). Blog post are good, particularly by top industry people (published techniques,papers,slides at conferences for instance), and better when they link papers.