v1.0.0

Split the roadmap out of [Unreleased] and say the section is empty

The top of the changelog read as if work were pending a release. It was not:
the eight entries under [Unreleased] are things not yet written, and everything
already shipped — click tracking included — is in [1.0.0].

Keep a Changelog, which this file declares it follows, reserves [Unreleased] for
changes already made and awaiting a version. A roadmap under that heading is a
category error, and it predates the tracking module.

[Unreleased] stays, now explicitly empty, because CONTRIBUTING.md:66 and :151 and
README.md:317 all tell contributors to add their entry there — removing it would
leave the next change with nowhere to go. The roadmap moves to its own section.