Made Server a singleton, accessible by Bukkit.getServer().

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/Bukkit.java

@@ -0,0 +1,39 @@
+
+package org.bukkit;
+
+/**
+ * Represents the Bukkit core, for version and Server singleton handling
+ */
+public final class Bukkit {
+    private static Server server;
+
+    /**
+     * Static class cannot be initialized.
+     */
+    private Bukkit() {
+    }
+
+    /**
+     * Gets the current {@link Server} singleton
+     *
+     * @return Server instance being ran
+     */
+    public static Server getServer() {
+        return server;
+    }
+
+    /**
+     * Attempts to set the {@link Server} singleton.
+     *
+     * This cannot be done if the Server is already set.
+     *
+     * @param server Server instance
+     */
+    public static void setServer(Server server) {
+        if (Bukkit.server != null) {
+            throw new UnsupportedOperationException("Cannot redelcare singleton Server");
+        }
+
+        Bukkit.server = server;
+    }
+}