* gl: amortize shader compilation over N frames
On platforms which don't support parallel shader compilation (e.g. Firefox), we
can sort of emulate it by queueing up any requests to `Material::compile()` and
compiling each shader over multiple frames.
Compiling over consecutive frames slows things quite noticeably. Instead, space
each compilation over a number of ticks (16 chosen arbitrarily).
If we need a program NOW, we can bump a program queued for much later to the
front. We also avoid compiling any queued programs on this same frame to limit
stuttering.
* gl: add flag to disable amortized shader compile
If this flag is on, the new amortized compile code should theoretically never be
executed.
* gl: add CompilerPriorityQueue docs, Java API
* gl: amortize shaders, z3moon feedback
* gl: update CompilerThreadPool
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