Change delimiter to also match Unicode Space Separators

[paulzzy]

See https://www.compart.com/en/unicode/category/Zs for a list of the
included characters.

Fixes #218.

[paulzzy]

I just realized that \p{Space_Separator} doesn't match tabs or newlines (and a couple other things covered by \s.

The tests pass regardless, but I added \s back in case it causes problems otherwise.

[paulzzy]

Also, I'd like to add tests for \p{Space_Separator}, where should I do that?

[inukshuk]

Sorry it took my a while to get to this!

I'd add tokenizer tests here. But since this is essentially a configuration option I'm not even sure that we should add too many specific tests. I'll merge this now, but you're welcome to add tests in a separate PR.