Pull changes to generate config using Go

I got frustrated trying to figure out how to get PyOpenSSL to actually verify the server's cert, so I ended up rewriting this in Go.  I also never liked the stateful nature of storing the certificates on disk, so now the config generator just checks all domains on each run.  Because I've parallelized the checks, I'm able to run through allsites.txt and generate the config files in under 4 seconds.

The big thing that's missing is the Amazon upload.  If we're okay with the rest of this, we can bring over the existing script for doing that and just use it as before.

I also still need to update the README.  I'm holding off on that until I get the green light on this approach.
Good catch on the additional extensions.  I'll filter those out too.

If cloud.yaml is authoritative, what is the process for adding a domain (with cert) to cloud.yaml?