Initial implementation of Promises.all, .any, .none, and .one class methods.
Renamed new Promise methods to all?, any?, none?, and on? (added question marks).
Merge branch 'master' into promise-all
Merge branch 'master' into promise-all
Removed Promise.one? and Promise.none?

The original request was for .any? and .all? methods. We added .none?
and .one? methods for synergy with arrays, but didn't like that these
methods supressed exceptions. So we decided to add only the requested
methods and consider other methods in the future.
Merge pull request #198 from ruby-concurrency/promise-all

Initial implementation of Promises.all? and Promise.any? class methods.