Major MariFX update:

- Complete RetroFX filter (downscale+palette).
 - Additional palettes, extending to the full range of 64.
 - Localization support (just English for now).
 - Better slider input (shift for 10x increments, alt for 5x increments)
 - Use nosave cvars for performance and so they don't end up in savegames.
 - A lot of cleanup.

shaders/glsl/mfx_retrofx.fp

@@ -0,0 +1,10 @@
+/*
+   RetroFX downscaling from MariENB
+   (C)2012-2021 Marisa Kirisame
+*/
+void main()
+{
+	// far more simplified when the actual scale calculations are on the zscript side
+	ivec2 ncoord = ivec2((floor(TexCoord*bresl)/bresl)*textureSize(InputTexture,0));
+	FragColor = texelFetch(InputTexture,ncoord,0);
+}