What's new:
* The style is consistent with the dark m.css theme that's used on the
website and so provides a bit better "brand identity".
* The canvas is responsive, looking properly on mobile and scaling down
with aspect ratio preservation if the screen is too narrow.
* It's now possible to override canvas size and aspect ratio or make it
"fullscreen", i.e. occupying the whole browser window.
* If the app crashes, a helpful message is printed instead of
everything just being stuck.
At the moment just the GL library itself w/o the tests, and without
backwards compatibility aliases. The following types were left in the
root namespace, despite being in the GL/ directory, as they will get
moved back soon:
* Image, CompressedImage and their dimensional typedefs
* ImageView, CompressedImageView and their dimensional typedefs
* PixelStorage
Not PixelFormat etc., that one will stay in the GL namespace and a
completely new PixelFormat enum will be provided in the root namespace.
Minimal updates (just the include guards) so Git is hopefully able to
detect the rename and track the history properly.
Everything except Magnum::GL doesn't compile now.