Improved starfields

game/modules/tome/class/FortressPC.lua

game/modules/tome/class/Game.lua

game/modules/tome/data/general/events/fearscape-portal.lua

...dules/tome/data/gfx/particles/shertul_fortress_engine.lua

game/modules/tome/data/gfx/particles/starfield.lua

game/modules/tome/data/gfx/shaders/starfield.frag

game/modules/tome/data/gfx/shaders/starfield.lua

game/modules/tome/data/zones/abashed-expanse/zone.lua

game/modules/tome/data/zones/eidolon-plane/zone.lua

.../modules/tome/data/zones/stellar-system-shandral/zone.lua

src/particles.c