Fix documentation regarding mouse wheel X & Y values

The documentation for EventHandler::on_mouse_wheel is wrong -- the
values are inverted from what they should be.
VisualUnitTest: Fix lack of window termination through WM close
EventHandler: Fix bug that led to duplicate window && mouse events

The lack of switch breaks at the end of the event's top-level switch
handlers led to duplicate events being fired, i.e.: two
SDL_MOUSEBUTTONUP events being fired for one. -_-
  This is a bug squash that has been plauging me for some time now!
Fix CMake Policy CMP0048 warning (version vars)

...regarding the usage of the reserved PROJECT_VERSION variables. I've
chosen to opt out (use old, pre-3.0 CMake behavior).
Fix cmake_policy err for ver < 3.0
platform.cmake: Use default installation path for OSX SDK
Fix compile err affecting Xcode generated project builds
Fix OSX SDK paths && update deps URL

* Use default OSX SDK paths.
* OSX dependencies have been moved to the osx sub-directory of
nomlib's project files.
travis-ci: Enable building of examples && disable exec of tests