Add raylib lua examples

examples/core_world_screen.lua

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+-------------------------------------------------------------------------------------------
+--
+--  raylib [core] example - World to screen
+--
+--  This example has been created using raylib 1.6 (www.raylib.com)
+--  raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+--
+--  Copyright (c) 2014-2016 Ramon Santamaria (@raysan5)
+--
+-------------------------------------------------------------------------------------------
+
+-- Initialization
+-------------------------------------------------------------------------------------------
+local screenWidth = 800
+local screenHeight = 450
+
+InitWindow(screenWidth, screenHeight, "raylib [core] example - 3d camera free")
+
+-- Define the camera to look into our 3d world
+local camera = Camera(Vector3(0.0, 10.0, 10.0), Vector3(0.0, 0.0, 0.0), Vector3(0.0, 1.0, 0.0), 45.0)
+
+local cubePosition = Vector3(0.0, 0.0, 0.0)
+
+local cubeScreenPosition = Vector2(0, 0)
+
+SetCameraMode(CameraMode.FREE)          -- Set a free camera mode
+SetCameraPosition(camera.position)      -- Set internal camera position to match our camera position
+SetCameraTarget(camera.target)          -- Set internal camera target to match our camera target
+SetCameraFovy(camera.fovy)              -- Set internal camera field-of-view Y
+
+SetTargetFPS(60)                        -- Set our game to run at 60 frames-per-second
+----------------------------------------------------------------------------------------
+
+-- Main game loop
+while not WindowShouldClose() do        -- Detect window close button or ESC key
+    -- Update
+    ------------------------------------------------------------------------------------
+    camera = UpdateCamera(camera)       -- Update internal camera and our camera
+    
+    -- Calculate cube screen space position (with a little offset to be in top)
+    cubeScreenPosition = GetWorldToScreen(Vector3(cubePosition.x, cubePosition.y + 2.5, cubePosition.z), camera)
+    ------------------------------------------------------------------------------------
+
+    -- Draw
+    ------------------------------------------------------------------------------------
+    BeginDrawing()
+
+        ClearBackground(RAYWHITE)
+
+        Begin3dMode(camera)
+
+            DrawCube(cubePosition, 2.0, 2.0, 2.0, RED)
+            DrawCubeWires(cubePosition, 2.0, 2.0, 2.0, MAROON)
+
+            DrawGrid(10, 1.0)
+
+        End3dMode()
+        
+        DrawText("Enemy: 100 / 100", cubeScreenPosition.x - MeasureText("Enemy: 100 / 100", 20)//2, cubeScreenPosition.y, 20, BLACK)
+        DrawText("Text is always on top of the cube", (screenWidth - MeasureText("Text is always on top of the cube", 20))//2, 25, 20, GRAY)
+
+    EndDrawing()
+    ------------------------------------------------------------------------------------
+end
+
+-- De-Initialization
+----------------------------------------------------------------------------------------
+CloseWindow()        -- Close window and OpenGL context
+----------------------------------------------------------------------------------------