Add info about dependencies
Add dist task for gulp
Use new options parameter for PIXI 2
Add example to show pixel ref images
Switch to PIXI.autoDetectRecommendedRenderer
Bump npm versions for karma, gulp-header, resemblejs
Reduced number of WebGL contexts created during tests

The normal testing suite creates and destroys many WebGL contexts during
testing.  However, browsers get grumpy if you make too many WebGL
contexts, and this was producing wierd failures. So tests were rewritten
to reduce the number of contexts created.