CRT shader library for the screen-fx-crt skill

Source: libretro/slang-shaders (RetroArch), category "crt" — the same library ShaderGlass ships:
  https://github.com/libretro/slang-shaders  (commit 2b0530bac0e8083d9d643c194929dc0a6b69bd35)
  ShaderGlass by mausimus (GPL-3.0): https://github.com/mausimus/ShaderGlass  (commit cdf68200d40ac124465396909b680f6e755604b7)

Four presets are shipped (the most recommended on the libretro forums and the emulation wiki):
  crt-guest-advanced-fast, crt-geom, crt-royale, newpixie-crt (its frame image is replaced by a blank 1x1 image).
Each was converted automatically (the build script is not included):
  Vulkan GLSL (.slang) -> SPIR-V (glslang) -> GLSL ES 3.00 (SPIRV-Cross), 2-D arrays flattened for WebGL2.
The shader code is the authors' work; each shader keeps its original license (mostly GPL-2.0+/GPL-3.0,
MIT or public domain) and credits — see the header of the original file listed in p/<id>.json -> "id"
under crt/ in the slang-shaders repository.
