Add mention of new operators

[LemmusLemmus]

Simply adds a mention of the new operators has and not-has in the book.

[fdncred]

While you're in here, would you mind adding like and not-like? like is a synonym for =~ and not-like is a synonym for !~.

[LemmusLemmus]

Sure!

Does my change look OK (using `=~` or `like` ) or would you prefer listing the synonyms on separate table rows?

_{BTW, `like` and `not-like` do not seem to be listed when running `help operators`.}

[fdncred]

Does my change look OK

I think it's fine. Thanks for adding it. If someone doesn't like it, they can submit a PR to change it. The key is that it's documented now.

BTW, like and not-like do not seem to be listed when running help operators.

Yup, that's a bug too. I wasn't quite sure how to add them.