[refactor] New buff framework (player implementation)

Get rid of `iConditionBitFlag` in favor of a system of individual buff
objects that get composited to a bitflag on-the-fly.
Buff objects can have callbacks for application, expiration, and tick,
making them pretty flexible. Scripting languages can eventually use
these for custom behavior, too.

TODO:
- Get rid of bitflag in BaseNPC
- Apply buffs from passive nano powers
- Apply buffs from active nano powers
- Move eggs to new system
- ???

src/EntityRef.hpp

@@ -0,0 +1,56 @@
+#pragma once
+
+#include "core/Core.hpp"
+
+/* forward declaration(s) */
+struct Entity;
+
+enum EntityKind {
+    INVALID,
+    PLAYER,
+    SIMPLE_NPC,
+    COMBAT_NPC,
+    MOB,
+    EGG,
+    BUS
+};
+
+struct EntityRef {
+    EntityKind kind;
+    union {
+        CNSocket *sock;
+        int32_t id;
+    };
+
+    EntityRef(CNSocket *s);
+    EntityRef(int32_t i);
+
+    bool isValid() const;
+    Entity *getEntity() const;
+
+    bool operator==(const EntityRef& other) const {
+        if (kind != other.kind)
+            return false;
+
+        if (kind == EntityKind::PLAYER)
+            return sock == other.sock;
+
+        return id == other.id;
+    }
+
+    bool operator!=(const EntityRef& other) const {
+        return !(*this == other);
+    }
+
+    // arbitrary ordering
+    bool operator<(const EntityRef& other) const {
+        if (kind == other.kind) {
+            if (kind == EntityKind::PLAYER)
+                return sock < other.sock;
+            else
+                return id < other.id;
+        }
+
+        return kind < other.kind;
+    }
+};