NS records publishing, performance and stability fixes

NS records are now published by the nameserver, both in standard DNS format and the DoT format proposed by facebook here:

https://tools.ietf.org/id/draft-bretelle-dprive-dot-spki-in-ns-name-00.html#formatting-dot-spki-in-name-server-name

Additionally, improvements to testing were made which resulted in some stability and performance improvements, particularly around how hostnames are generated, which would only be an issue with larger (200+ nodes) networks.

Packages for Windows are now available.

Docker, Linux, and OS X (via homebrew tap @ https://github.com/zerotier/homebrew-tap) packages are still available.