* wip: add rect area light in example
* fix normal not normalized
* update example
* fix light accumulation for custom light in deferred renderer
* fix alpha is larger than 1 in the light accumulation
* naming tweaks
* updateOffset in deferred renderer
* convert albedo color to sRGB in gbuffer
* support depth attachment in gbuffer
* fix some shadow map issue in deferred renderer
* clear depth buffer after render
* update pcf kernel in shadow
* fix light accumulate
* fix pcf shadow in deferred renderer
* deferred: fix pcss
* respect to material linear
* can disable camera bounding box intersection in shadowmap
* deferred: show black when there is no light
* resize support pixelRatio
* release alpha.18
* wip: upgrade to webgl2
* update shaders to version 300
* fix index for texture must be constant in webgl 2
* remove npot
* fix naming conflicts of using texture previously
* fix wrong internal format in float textures.
* fix depth texture format
* fix texture enabled define
* fix instancing
* fix some cases
* fix some case use extension
* fix frag depth
* tweak
* generate mimap for NPOT texture
* remove debugger code
* fix alchemyao case
* fix ssr case
* not generate mipmap in compositor by default.