native support for running as a Windows service?

[slingamn]

@zaher successfully wrapped Oragono on Windows with nssm; there's also https://github.com/kohsuke/winsw. However, we may want to add native support for running as a Windows service, with something like https://github.com/judwhite/go-svc.

If we decide against this, we may want to write a manual entry describing how to configure one of the wrappers like nssm.

[zaher]

We used Oragono for year as Debian services worked stable, then our company moved to use Windows server, Installed it using nssm, it is easy for owner of company, but still make it not easy that we need to install 2 projects instead of one,
with nssm we it is running stable for another year too, supporting clients inside a real project.

With built in service for windows Oragono will be completed beside a full of features that we need.