Implements World.save and Server.savePlayers()

By: Morgan Humes <mrh9724@lanaddict.com>

paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java

@@ -297,4 +297,8 @@ public final class CraftServer implements Server {
             return null;
         }
     }
+
+    public void savePlayers() {
+        server.d();
+    }
 }

paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java

@@ -474,4 +474,12 @@ public class CraftWorld implements World {
 
         return list;
     }
+
+    public void save() {
+        // Writes level.dat
+        world.r();
+
+        // Saves all chunks/regions
+        world.o.a(true, null);
+    }
 }