Updated PixiShader to use standard uniform naming conventions (1f, 2f, 2fv, etc). Added support for multiple sampler2D calls, allowing multi-texture shaders. Added support for Linear, Repeat, Nearest, Audio and Keyboard textures. Updated all the examples to use the new uniform naming convention. Updated Gruntfile to use the renamed GrayFilter and fixed indexAll in Example 15 to use the GrayFilter as well.
Fixed typo in AbstractFilter (unifroms to uniforms)
Made sampler2D check more robust.
Dramatically refactored PixiShader. Significantly smaller, less branching, much faster sync loop and no constant texture uploads.
Merge branch 'pr/406' into dev

Conflicts:
	bin/pixi.dev.js
	bin/pixi.js
	src/pixi/renderers/webgl/PixiShader.js
Merged new PIXI Shader code