Add (3.0) [core] examples

[Andre-LA]

• [x] core_basic_window
• [ ] core_basic_window_web
• [x] core_input_keys
• [x] core_input_mouse
• [x] core_input_mouse_wheel
• [x] core_input_gamepad
• [ ] core_input_multitouch
• [ ] core_input_gestures
• [x] core_2d_camera
• [x] core_2d_camera_platformer
• [x] core_3d_camera_mode
• [x] core_3d_camera_free
• [x] core_3d_camera_first_person
• [x] core_3d_picking
• [x] core_world_screen
• [x] ~~core_custom_logging~~
• [x] core_window_letterbox
• [x] core_drop_files
• [x] core_random_values
• [x] core_scissor_test
• [x] core_storage_values
• [x] core_vr_simulator
• [x] core_loading_thread