[Input] Legacy keyboard respects the KeyRepeat field.

If the legacy keyboard device receives a key down event with IsRepeat set it
will only raise it's own key down event if it's KeyRepeat field is set to true.

This is as documented, regression casused by refactoring. Fixes issue #201.

Also change the GameWindowState example to show setting of KeyRepeat to true
and false and how that changes the event counts for the legacy and new keyboard
devices.
Merge pull request #202 from Frassle/issue201

[Input] Legacy keyboard respects the KeyRepeat field.

Fixes #201.
[Input] Add IsAnyKey/ButtonDown/Pressed to input state.

Adds properties to KeyboardState, MouseState, JoystickState and GamePadState
(GamePadButtons), to see if any key or button is down. This should be faster
than iterating over all the public IsDown properties as we can make use of the
internal bit fields.

GamePadButtons uses IsButtonPressed rather than IsButtonDown like the others as
it more closely matches it's current interface (no down methods).