Fiber examples and Windows support

I added a bunch of examples to help refine some of the libdex APIs.

Additionally, I added support for the Windows Fibers API which brings our support matrix up to Linux, macOS, FreeBSD (possibly some other BSDs too), Illumos, Hurd, and now Windows.

I know there are a few things I’d like to still add and change the APIs, but I guess now it’s at the point where it’s time to start building things with it. I’m likely to target pieces of Builder which have a lot of complex async callback chains. Those are likely to benefit the most from fibers.