Disallow inheriting of the null and windows mouse/keyboard/pad handlers. These aren't intended to be further extended.
Move Keyboard/Mouse/Pad handlers over to using vector.
Move the mouse/keyboard/pad handlers over to using unique_ptr as the underlying base.
Fix stupid mistake I made with rebasing.

Accidentally overwrote the Pad handler stuff for windows. Should be fixed now.
Merge pull request #150 from lioncash/unique-ptr

Misc cleanup of the Io stuff.