Fixed issue #212 by adding mouse module for visibility with testing

[kurttepelikerim]

Created a method to hide mouse directly from Pygame Zero with testing addressed in issue #212.

[lordmauve]

We don't need to do this because people can just write

from pygame import mouse
mouse.set_visible(False)

To add value we could either

• Document this usage, including how to import from pygame (and maybe how and why to import - the docs are for beginners)
• Add an even easier to use object. We already have mouse but it is an Enum. We could add more methods like

>>> mouse.current_pos 
(548, 139)
>>> mouse.visible
False
>>> mouse.visible = not mouse.visible
>>> mouse.recent_pos
collections.deque([(521, 119), (538, 127), (548, 139)])

I quite like the latter idea because it would let us map mouse buttons to our constants, among other things.