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!
If you have two columns you want to extract data into, you need to have two regex captures.  I couldn't think of a great way to express that though, suggestions welcome!