Adding support for osx and win 64 bit builds.

* Change osx to osx32
* Change win to win32
* Change defaults from ['osx', 'win'] to ['osx32', 'osx64', 'win32', 'win64']
* Tried to hit some checks I missed.
* Change osx.json to osx32.json and win.json to win32.json
* Got failing tests down to 5....
* Re-adding support for 'osx' and 'win' to avoid breaking changes
* Check for 'osx' and 'win' in the platforms list and replace them with 'osx32', 'osx64', and 'win32', 'win64' respectively.
* Fix tests.
* Add linux shorthand to compliment win and osx shorthand.
* Add fix for detecting Windows 64-bit.
* Update platform-overrides dependency to ~1.0.0
* Add win, osx, linux and description of what they do to readme.