Added Mouse Integration

[mheller575]

Added support for mouse menu selections.

• Support mouse position for current selected item. As mouse passes over text control, control is set to currently selected item.
• Support mouse click for menu item action execution. Clicking within a text control boundary will run the action for that item.
• Support mouse scroll wheel for current selected item. Same behavior as the up and down arrows, just implemented from the scroll wheel.

Implements enhancement request #2 https://github.com/ParadoxZero/GameMenu-cpp/issues/2