Specbook 0.8.0: browser extension for live calls

Live calls from a hosted Specbook page no longer need an API that allows CORS. A new browser extension makes the call for you, with your permission for each API.

• A browser extension for Chromium browsers on a computer. It is attached to this release as specbook-extension-chromium-0.8.0.zip; the install steps are on https://docs.specbook.dev/reference/browser-extension/. It asks for nothing when you install it. The first live call to an API fails with an Allow button, and a grant belongs to one site and one API. It reads only until you also allow Modify data (POST, PUT, PATCH and DELETE), sends no cookies, and every grant can be revoked.
• The offer is in the failed response. A call the browser blocked says the extension can send it. A call it has not been allowed to make shows Allow, and a refused change shows Allow modifying data. A response that came through the extension says via extension and carries an x-specbook-via header.
• One list in the extension's window. The API being asked about is highlighted, with a Modify data box beside Allow, so reading and modifying can be allowed in one answer.
• @specbook/core: a failed step can say what a page can offer (StepResult.errorHint), and the extension's wire protocol and its dispatcher are available as @specbook/core/wire.
• Docs: a reference page for the extension and its privacy policy, and variables explained: {petId} in a spec is the path parameter, {{petId}} is a Specbook variable.

The extension is not in a store yet. Until it is, unzip it and load it unpacked (turn on Developer mode in chrome://extensions).

No breaking changes.

Full Changelog: v0.7.0...v0.8.0