Implement Brigadier Mojang API

This is the start of a new module for Paper to add support for API's
that interface Mojang API's directly.

This allows us to version properly by MC version incase Mojang makes any major breaking changes.

It also lets us separate Mojang API's from Paper-API so our downstream friends at Glowstone
will not have to worry about Mojang code.

Adds AsyncPlayerSendCommandsEvent
  - Allows modifying on a per command basis what command data they see.

Adds CommandRegisteredEvent
  - Allows manipulating the CommandNode to add more children/metadata for the client

Spigot-API-Patches/0001-POM-changes.patch

@@ -1,11 +1,11 @@
-From 755a3e8943286365b0f518c5423687872c8181ae Mon Sep 17 00:00:00 2001
+From 72e2e4af618fca06282903aa0100a779f2945168 Mon Sep 17 00:00:00 2001
 From: Zach Brown <zach.brown@destroystokyo.com>
 Date: Tue, 1 Mar 2016 00:16:08 +0100
 Subject: [PATCH] POM changes
 
 
 diff --git a/pom.xml b/pom.xml
-index 8964b9e33..ce09baeab 100644
+index 8964b9e3..ce09baea 100644
 --- a/pom.xml
 +++ b/pom.xml
 @@ -2,34 +2,28 @@
@@ -110,6 +110,19 @@ index 8964b9e33..ce09baeab 100644
                      <!-- when downloading via Maven we can pull depends individually -->
                      <shadedArtifactAttached>true</shadedArtifactAttached>
                  </configuration>
+diff --git a/src/main/java/org/bukkit/event/player/PlayerEvent.java b/src/main/java/org/bukkit/event/player/PlayerEvent.java
+index 793b661b..b7c8f2c3 100644
+--- a/src/main/java/org/bukkit/event/player/PlayerEvent.java
++++ b/src/main/java/org/bukkit/event/player/PlayerEvent.java
+@@ -14,7 +14,7 @@ public abstract class PlayerEvent extends Event {
+         player = who;
+     }
+ 
+-    PlayerEvent(@NotNull final Player who, boolean async) {
++    public PlayerEvent(@NotNull final Player who, boolean async) { // Paper - wtf?
+         super(async);
+         player = who;
+ 
 -- 
-2.25.1
+2.26.2