Performance improvements

[w0rm]

Closes #23 and #26

This PR improves webgl performance by reducing the number of gl calls. For more information click here

• the uniforms are diffed using === to avoid reuploading common scene parameters like camera matrix or lights
• attribute locations are cached so that they don't have to be retrieved for every draw call
• webgl rendering settings are diffed against the JavaScript snapshot

Most of this was done together with @ianmackenzie. He also set up a test scene using the soon-to-be-released elm-3d-scene package, that we used to benchmark the performance:

@MartinSStewart, who had opened the original issue, provided the source code of his game. Here you can see that it got slightly better:

Here you can see the absence of redundant calls:

There were a lot of bugs, because of the stateful nature of webgl. In order to ensure that it works, I tested it using the following projects:

• https://github.com/elm-explorations/webgl/tree/master/examples
• https://github.com/ianmackenzie/elm-3d-scene/tree/master/examples
• https://github.com/ianmackenzie/elm-3d-scene/tree/master/testing
• https://github.com/justgook/webgl-playground/tree/master/examples
• https://gitlab.com/MartinSStewart/hackman/
• https://github.com/nacmartin/elm-webgl-lessons
• https://github.com/w0rm/elm-mogee
• https://github.com/w0rm/elm-physics/tree/master/examples
• https://github.com/w0rm/elm-street-404
• https://github.com/w0rm/elm-webgl-playground