Added EAB (External Account Binding) Support

[rtgibbons]

This was done via a pull request on acme-tiny. In doing so you can now use EAB from CA Providers likes ZeroSSL and BuySSL. This is apart of the ACME protocol, just not something Let's Encrypt has implemented.

In doing this, I made the script naming, logging more generic.

I went ahead and did a file rename on the original letsencrypt script so the Diff is clean. But if you'd rather change this to be a separate script , let me know and I can send another pull request.

This also includes the fix form #275 , since the script won't work without it.