crush depth

No More OpenGL

I'm dropping OpenGL in favour of Vulkan.

No more broken drivers (probably). No more dealing with source code level management of shader code at runtime (no more sombrero). No more broken GLSL shader compilers, for that matter. No more weak typing (no more jcanephora). No more logarithmic depth buffer - Vulkan has reversed floating-point depth buffers accessible without extensions.

Planning to rewrite r2 using Vulkan, yielding r3. A few design issues that were imposed by the OpenGL 3.3 core requirement can be corrected.

Still need to give the Vulkan API a friendly face though, to make it feel like a Java API instead of a C++ API.