Fixes user_supplied callbacks #37

This PR fixes #37 and the event tests are executed on all available platforms.

It looks like the original problem with seqfaults on AMD (and Nvidia) for that matter was that you can't modify something outside your closure in a cfunction. By using the libuv async callback this should work properly.

Also this is some of the groundwork necessary for #35 

Tested on AMD APP SDK (Intel CPU) and NVIDIA.

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@jakebolewski What is the difference between ````queued```` and ````submitted````? Do you have a specific reason why we should get ````queued```` back?