Project modernization (#630)

* Fixed boats falling and a TP glitch #266

* Replaced every C-style cast with C++ ones

* Replaced every C-style cast with C++ ones

* Fixed boats falling and a TP glitch #266

* Updated NULL to nullptr and fixing some type issues

* Modernized and fixed a few bugs

- Replaced most instances of `NULL` with `nullptr`.
- Replaced most `shared_ptr(new ...)` with `make_shared`.
- Removed the `nullptr` macro as it was interfering with the actual nullptr keyword in some instances.

* Fixing more conflicts

* Replace int loops with size_t and start work on overrides

Minecraft.World/RemoveEntitiesPacket.h

@@ -21,7 +21,7 @@ public:
 	virtual int getEstimatedSize();
 
 public:
-	static shared_ptr<Packet> create() { return shared_ptr<Packet>(new RemoveEntitiesPacket()); }
+	static shared_ptr<Packet> create() { return std::make_shared<RemoveEntitiesPacket>(); }
 	virtual int getId() { return 29; }
 };