Add (low level) functionality to allow rendering 3D Meshes.

- Add love.graphics.setDepthMode(testcomparison, enablewrites).
- Add love.graphics.setMeshCullMode.
- Add love.graphics.setFrontFaceWinding.

Depth testing and depth writes require a depth buffer to work. The mesh cull mode controls whether front/back faces of a mesh are culled. The front face winding determines whether a clockwise or counterclockwise-oriented face in a mesh is considered front facing.

--HG--
branch : minor

src/modules/graphics/vertex.h

@@ -86,6 +86,14 @@ enum AttributeStep
 	STEP_MAX_ENUM
 };
 
+enum CullMode
+{
+	CULL_NONE,
+	CULL_BACK,
+	CULL_FRONT,
+	CULL_MAX_ENUM
+};
+
 namespace vertex
 {
 
@@ -106,6 +114,13 @@ enum DataType
 	DATA_MAX_ENUM
 };
 
+enum Winding
+{
+	WINDING_CW,
+	WINDING_CCW,
+	WINDING_MAX_ENUM
+};
+
 enum class TriangleIndexMode
 {
 	NONE,
@@ -305,6 +320,14 @@ bool getConstant(const char *in, DataType &out);
 bool getConstant(DataType in, const char *&out);
 std::vector<std::string> getConstants(DataType);
 
+bool getConstant(const char *in, CullMode &out);
+bool getConstant(CullMode in, const char *&out);
+std::vector<std::string> getConstants(CullMode);
+
+bool getConstant(const char *in, Winding &out);
+bool getConstant(Winding in, const char *&out);
+std::vector<std::string> getConstants(Winding);
+
 } // vertex
 
 typedef vertex::XYf_STf_RGBAub Vertex;