adding the missing press checks in the core_input_mouse example:
I added the missing MOUSE_BUTTON_SIDE,MOUSE_BUTTON_EXTRA,MOUSE_BUTTON_FORWARD,MOUSE_BUTTON_BACK press checks.
note: my mouse doesn't have the "forward" and "back" buttons, so I couldn't test if they work
* Added core_input_keys example
* Added core_basic_window example
* Added core_input_mouse example
* Added core_input_mouse_wheel example
* Added Rectangle struct
* Added core_input_gestures example to utilize the Rectangle struct
* Removed unused imports
* Used the right draw function for the example
* PEP8 fixes
* Added core 2d camera examples
* Added core 2d camera examples