Fix bugs and fix #4

Particles can no longer spawn under the world.
Particles no longer spawn in blocks, instead spawning in air.
Fixed bug present since 1.2.0, which meant particle amount was dependant on blocks around player.
New particle multiplier allowing greater control of particle amount.
New F3 screen text, allows user to debug particle amount.
Removed upper and lower limit buttons.

src/main/resources/dust.mixins.json

@@ -4,7 +4,8 @@
   "package": "net.lizistired.cavedust.mixin",
   "compatibilityLevel": "JAVA_16",
   "mixins": [
-    "ClientWorldAccessor"
+    "ClientWorldAccessor",
+    "MixinDebugScreenOverlay"
   ],
   "client": [
   ],