Upgrade fuq.h to v1.3.0
NUB_DEBUG was a dumb choice

Should just use DEBUG for simplicity.
Accept cb for nub_thread_dispose

To enable easier cleanup of resources, allow a callback to be passed
that will run after the thread has been joined and internal resources
have been cleaned up. (this does exclude the uv_close finishing on the
uv_async_t)
Add nub_thread_join

In case the thread should be disposed on the event loop thread, use
nub_thread_join as a blocking call to cleanup a thread's resources.
Misc fixes

* Forgot to rename a variable after changing the API.
* Add comment about needing to fix memory allocations.
* Add comment about fixing intermittent test race condition.