Changing examples to use makefile

- Testing a modified version of the makefile from raylib Instead of multiple project files for examples.
- Fixed readme example

Examples/core/core_3d_picking.cs

@@ -0,0 +1,7 @@
+using Raylib;
+using static Raylib.Raylib;
+
+public partial class Examples
+{
+    /*******************************************************************************************
    *
    *   raylib [core] example - Picking in 3d mode
    *
    *   This example has been created using raylib 1.3 (www.raylib.com)
    *   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
    *
    *   Copyright (c) 2015 Ramon Santamaria (@raysan5)
    *
    ********************************************************************************************/
    
    
    public static void Main()
    {
        // Initialization
        //--------------------------------------------------------------------------------------
        int screenWidth = 800;
        int screenHeight = 450;
    
        InitWindow(screenWidth, screenHeight, "raylib [core] example - 3d picking");
    
        // Define the camera to look into our 3d world
        Camera camera;
        camera.position = new Vector3( 10.0f, 10.0f, 10.0f );; // Camera position
        camera.target = new Vector3( 0.0f, 0.0f, 0.0f );;      // Camera looking at point
        camera.up = new Vector3( 0.0f, 1.0f, 0.0f );;          // Camera up vector (rotation towards target)
        camera.fovy = 45.0f;                                // Camera field-of-view Y
        camera.type = CAMERA_PERSPECTIVE;                   // Camera mode type
    
        Vector3 cubePosition = { 0.0f, 1.0f, 0.0f };
        Vector3 cubeSize = { 2.0f, 2.0f, 2.0f };
    
        Ray ray = {0.0f, 0.0f, 0.0f};        // Picking line ray
    
        bool collision = false;
    
        SetCameraMode(camera, CAMERA_FREE); // Set a free camera mode
    
        SetTargetFPS(60);                   // Set our game to run at 60 frames-per-second
        //--------------------------------------------------------------------------------------
    
        // Main game loop
        while (!WindowShouldClose())        // Detect window close button or ESC key
        {
            // Update
            //----------------------------------------------------------------------------------
            UpdateCamera(&camera);          // Update camera
    
            if (IsMouseButtonPressed((int)Mouse.LEFT_BUTTON))
            {
                ray = GetMouseRay(GetMousePosition(), camera);
    
                // Check collision between ray and box
                collision = CheckCollisionRayBox(ray,
                            new BoundingBox((Vector3){ cubePosition.x - cubeSize.x/2, cubePosition.y - cubeSize.y/2, cubePosition.z - cubeSize.z/2 );,
                                          new Vector3( cubePosition.x + cubeSize.x/2, cubePosition.y + cubeSize.y/2, cubePosition.z + cubeSize.z/2 }););
            }
            //----------------------------------------------------------------------------------
    
            // Draw
            //----------------------------------------------------------------------------------
            BeginDrawing();
    
                ClearBackground(RAYWHITE);
    
                BeginMode3D(camera);
    
                    if (collision)
                    {
                        DrawCube(cubePosition, cubeSize.x, cubeSize.y, cubeSize.z, RED);
                        DrawCubeWires(cubePosition, cubeSize.x, cubeSize.y, cubeSize.z, MAROON);
    
                        DrawCubeWires(cubePosition, cubeSize.x + 0.2f, cubeSize.y + 0.2f, cubeSize.z + 0.2f, GREEN);
                    }
                    else
                    {
                        DrawCube(cubePosition, cubeSize.x, cubeSize.y, cubeSize.z, GRAY);
                        DrawCubeWires(cubePosition, cubeSize.x, cubeSize.y, cubeSize.z, DARKGRAY);
                    }
    
                    DrawRay(ray, MAROON);
                    DrawGrid(10, 1.0f);
    
                EndMode3D();
    
                DrawText("Try selecting the box with mouse!", 240, 10, 20, DARKGRAY);
    
                if(collision) DrawText("BOX SELECTED", (screenWidth - MeasureText("BOX SELECTED", 30)) / 2, screenHeight * 0.1f, 30, GREEN);
    
                DrawFPS(10, 10);
    
            EndDrawing();
            //----------------------------------------------------------------------------------
        }
    
        // De-Initialization
        //--------------------------------------------------------------------------------------
        CloseWindow();        // Close window and OpenGL context
        //--------------------------------------------------------------------------------------
    
        return 0;
    }
        
+}