Readd core examples

examples/core/input_mouse_wheel.zig

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+//
+// input_mouse_wheel
+// Zig version: 
+// Author: Nikolas Wipper
+// Date: 2020-02-16
+//
+
+const rl = @import("raylib");
+
+pub fn main() anyerror!void
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const screenWidth = 800;
+    const screenHeight = 450;
+
+    rl.InitWindow(screenWidth, screenHeight, "raylib-zig [core] example - basic window");
+
+    var boxPositionY: f32 = screenHeight / 2 - 40;
+    var scrollSpeed: f32 = 4;            // Scrolling speed in pixels
+
+    rl.SetTargetFPS(60);               // Set our game to run at 60 frames-per-second
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!rl.WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        boxPositionY -= (rl.GetMouseWheelMove() * scrollSpeed);
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        rl.BeginDrawing();
+
+            rl.ClearBackground(rl.WHITE);
+
+            rl.DrawRectangle(screenWidth/2 - 40, @floatToInt(c_int, boxPositionY), 80, 80, rl.MAROON);
+
+            rl.DrawText("Use mouse wheel to move the cube up and down!", 10, 10, 20, rl.GRAY);
+            rl.DrawText(rl.FormatText("Box position Y: %03i", @floatToInt(c_int, boxPositionY)), 10, 40, 20, rl.LIGHTGRAY);
+
+        rl.EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    rl.CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+}
+