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.
- Better use either #ifdef #else #endif rather than commented code.
- We're sure we want to do some some "tonemapping" as you're not using HDR inputs, doesn't make much sense too me, we're loosing a lot of signal there ?  My understanding is that you do tonemapping after the bloom.
( http://mynameismjp.wordpress.com/2010/04/30/a-closer-look-at-tone-mapping/ (note that his "signal processing" series primer for post-processing is a good read, and his "bokeh" sample contains nice bloom code inside))