Additional Mouse/Keyboard commands

[Lunasole]

I'd like to suggest several commands to mouse and keyboard libs.

Keyboard
1. There are KeyboardInkey(), KeyboardPushed (), KeyboardReleased () functions, but it lacks something like KeyboardDown () to detect when key just was pressed.

Mouse
1. There are #PB_MouseButton_Left, #PB_MouseButton_Right, #PB_MouseButton_Middle constants to use with MouseButton(), but it lacks #PB_MouseButton4, #PB_MouseButton5 - those 4 and 5 are common in many modern mouses so would be good to add their handling too.
2. Additionally, mouse commands equivalents to those keyboard/key state commands


Surely it all could be easy implemented, but more beautiful if present in std lib for usefulness