rename `keyboard_key_down` or `keyboard_key_released` or both

[Frimkron]

The keyboard key functions are keyboard_key_down and keyboard_key_released, but the least-surprising opposite to keyboard_key_down would be keyboard_key_up, and the least-surprising opposite to keyboard_key_released would be keyboard_key_pressed. I suggest the functions are renamed for better memoribility. In addition I think the keyboard_ prefix is unnecessary.