Allow functions to be passed in ignore option

[cheapsteak]

Addresses #1

I would like to be able to tell findAndReplace to ignore certain nodes if they contain a class (like <p class="skip-me"/>), or if their style includes some css property

This PR switches to use unist-util-is, which already handles that

[wooorm]

Thanks! As discussed in #1, I do think it makes more sense that this feature lands in hast-util-is-element, so that other tools also benefit from it. I’m currently pushing [email protected], which will bubble through to this project without the need of any changes here: npm install will update it automatically.

Thanks for your work tho!