Create a list with an optional signup form, welcome email, and newsletter site

Create a list. Set form_enabled to publish a hosted double opt-in signup form at form.url; form_from is the sender (on a verified domain) of the confirmation email, and redirect_url is an optional https page to show after confirming. welcome ({ enabled, subject, and html, markdown, or a block document in content }) sends one welcome email, from form_from, when someone confirms. site ({ enabled, slug, title, description, accent }) publishes a public newsletter site at https://sendhq.cc/n/<slug> with a signup form, every issue sent with web.enabled, and an RSS feed at /n/<slug>/feed.xml; it needs the signup form on, and a slug that is reserved or taken returns 409. A workspace may have 100 lists.