How do I ... combine two columns (with formatting)

[kamilm]

First: Thanks for all the work on this package, it's a joy to work with and the docs are great as well!

I would like to combine two columns, say, mean and std into a single column within table and have it separated with a "plus-minus". Currently I am doing this before GT but doing this within GT could potentially lead to more advanced formatting, much like LaTeX where we can align on a decimal or, in my case, the "plus-minus" symbol. Is there a way to do this?