Extract verb, to extract data from one column into multiple columns

I often want to extract just part(s) of a data column rather than always separating the whole thing and then later throwing parts of it away.  This implements an `extract` verb for tidyr to do just that.

Thanks for this package, I look forward to using it!
That makes sense to me, the structure was a holdover from the if else in separate.  I will change it.