Add xmlrpc gem
Add xmlrpc gem

This was extracted from the Ruby 2.3 standard library to this gem.  See [Ruby 2.4 Release Announcement](https://www.ruby-lang.org/en/news/2016/12/25/ruby-2-4-0-released/)

MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,pellaea/mushroom-observer,MushroomObserver/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,JoeCohen/mushroom-observer,pellaea/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,pellaea/mushroom-observer,JoeCohen/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer