PaperPR - Projectile load/save limit per chunk

- Dropped "Add option to disable saving projectiles to disk" in favor of the above patch
 - Config migration is automatic. If "gameplay-mechanics.save-projectiles-to-disk" was set to false in purpur.yml, "projectile-load-save-per-chunk-limit" will be set to 0 in paper.yml (resulting in unchanged behaviour)

patches/server/0136-Arrows-should-not-reset-despawn-counter.patch

@@ -0,0 +1,21 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: William Blake Galbreath <Blake.Galbreath@GMail.com>
+Date: Wed, 4 Nov 2020 13:12:50 -0600
+Subject: [PATCH] Arrows should not reset despawn counter
+
+This prevents keeping arrows alive indefinitely (such as when the block
+the arrow is stuck in gets removed, like a piston head going up/down)
+
+diff --git a/src/main/java/net/minecraft/server/EntityArrow.java b/src/main/java/net/minecraft/server/EntityArrow.java
+index 7f89b269e3..5ec8c9484d 100644
+--- a/src/main/java/net/minecraft/server/EntityArrow.java
++++ b/src/main/java/net/minecraft/server/EntityArrow.java
+@@ -243,7 +243,7 @@ public abstract class EntityArrow extends IProjectile {
+         Vec3D vec3d = this.getMot();
+ 
+         this.setMot(vec3d.d((double) (this.random.nextFloat() * 0.2F), (double) (this.random.nextFloat() * 0.2F), (double) (this.random.nextFloat() * 0.2F)));
+-        this.despawnCounter = 0;
++        // this.despawnCounter = 0; // Purpur - do not reset despawn counter
+     }
+ 
+     @Override