add Filter2D for chaining postprocessing (2d transformation) 
+ some samples
+ asset_pack loader
viewport: inject _PixelSizel, _Near, _Far (+refactor injection to use beforeEach instead of autoData)
Mesh: split injectAndDraw into inject(...) and draw(...)
shaders: update default.vert to include comment about other common uniforms, attributes, varying
* fix bug : diseable all attribs when no longer use a program
* ProgramRunner no longer manage FBO (should be enabled in before section)
* add RequestRunOn.beforeEach
* add RequestRunOn.atEach
shaders: add deferred (normals, vertices) + depth_light
demo: normalized names used in shaders
demo: lot of internal changes ...
* used asset_pack to load Filter2D, ShaderProgram (not the editable one) , include a progressbar + log
* write a Renderer2 to support filter2d, pseudo-deferred rendering (used by SSAO)
* create & used Geometry and Material class
* activate a SSAO
demo: add TODO section into index.dart