added "pause" and "resume" to swipe API

It's a little different from this pull request: https://github.com/bradbirdsall/Swipe/pull/253
In my pull request "pause" and "resume" really do pause and resume if the swipe is not stopped; they don't do anything if it's in stopped state.
In https://github.com/bradbirdsall/Swipe/pull/253 "resume" make a stopped swipe to slide again.