Gen: Moved PiecePool into a separate file.

Also rewritten the PieceGenerator to use std::unique_ptr.

src/Generating/PrefabStructure.h

@@ -10,7 +10,7 @@
 #pragma once
 
 #include "GridStructGen.h"
-#include "PieceGenerator.h"
+#include "PiecePool.h"
 
 
 
@@ -25,12 +25,10 @@ public:
 	cPrefabStructure(
 		int a_GridX, int a_GridZ,
 		int a_OriginX, int a_OriginZ,
-		cPlacedPieces & a_Pieces,
+		cPlacedPieces && a_Pieces,
 		cTerrainHeightGenPtr a_HeightGen
 	);
 
-	virtual ~cPrefabStructure();
-
 protected:
 	/** The pieces placed by the generator. */
 	cPlacedPieces m_Pieces;