Adapt String.words to handle blank text in a more standard way.

[jbrains]

I propose providing a function for words that answers [] for blank text, because there are no words in a blank piece of text and because the empty string is, by common understanding, not a word.

I don't like the way I wrote the test, because I couldn't figure out how to fuzz a non-blank multiline string. I'd be very happy to take your suggestions about how to do that.

Since this is my first contribution, I don't know what I might have done that goes against house conventions. Just tell me what you need me to change, if anything.