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_input_keys.cs

@@ -0,0 +1 @@
+using Raylib;
using static Raylib.Raylib;

public partial class Examples
{
    /*******************************************************************************************
    *
    *   raylib [core] example - Keyboard input
    *
    *   This example has been created using raylib 1.0 (www.raylib.com)
    *   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
    *
    *   Copyright (c) 2014 Ramon Santamaria (@raysan5)
    *
    ********************************************************************************************/
    
    
    public static void Main()
    {
        // Initialization
        //--------------------------------------------------------------------------------------
        int screenWidth = 800;
        int screenHeight = 450;
    
        InitWindow(screenWidth, screenHeight, "raylib [core] example - keyboard input");
    
        Vector2 ballPosition = new Vector2( (float)screenWidth/2, (float)screenHeight/2 );
    
        SetTargetFPS(60);       // Set target frames-per-second
        //--------------------------------------------------------------------------------------
    
        // Main game loop
        while (!WindowShouldClose())    // Detect window close button or ESC key
        {
            // Update
            //----------------------------------------------------------------------------------
            if (IsKeyDown((int)Key.RIGHT)) ballPosition.x += 2.0f;
            if (IsKeyDown((int)Key.LEFT)) ballPosition.x -= 2.0f;
            if (IsKeyDown((int)Key.UP)) ballPosition.y -= 2.0f;
            if (IsKeyDown((int)Key.DOWN)) ballPosition.y += 2.0f;
            //----------------------------------------------------------------------------------
    
            // Draw
            //----------------------------------------------------------------------------------
            BeginDrawing();
    
                ClearBackground(RAYWHITE);
    
                DrawText("move the ball with arrow keys", 10, 10, 20, DARKGRAY);
    
                DrawCircleV(ballPosition, 50, MAROON);
    
            EndDrawing();
            //----------------------------------------------------------------------------------
        }
    
        // De-Initialization
        //--------------------------------------------------------------------------------------
        CloseWindow();        // Close window and OpenGL context
        //--------------------------------------------------------------------------------------

    }    
}