This commit adds support for SIMD-based alpha blending, which speeds up
the alpha-compositing of the nitpicker GUI server by circa 300% on ARM
Neon and x86_64 using SSE4.1
Issue #5428
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082