v0.2 - zoom, enhance and one setting to rule them all

This release adds a number of useful features such as a default client URL placeholder,
ability to redirect to the front-end URLs when viewing a page in the Wagtail admin, and
an option to redirect the preview to the client URL rather than use the default iframe embed mechanism.

A big change is the move to a single, namespaced settings dictionary - WAGTAIL_HEADLESS_PREVIEW:

WAGTAIL_HEADLESS_PREVIEW = {
    "CLIENT_URLS": {},  # previously HEADLESS_PREVIEW_CLIENTS_URLS
    "LIVE_PREVIEW": False,  # previously HEADLESS_PREVIEW_LIVE
    "SERVE_BASE_URL": None,  # new optional setting for HeadlessServeMixin / HeadlessMixin
    "REDIRECT_ON_PREVIEW": False,  # new optional setting to redirect the preview to the client preview URL
}

We added the HeadlessServeMixin and HeadlessMixin mixins for a fuller headless experience. HeadlessMixin is a combination of HeadlessPreviewMixin and HeadlessServeMixin. The latter changes the Page.serve() method to redirect the page to the front-end URL rather than try to render it. With this, the "View live" buttons in the Wagtail admin are usable again 🥳

Finally, the project structure has changed, with tests moving to the project root and the source code to src/. This should make for smaller packaged releases 🌍

Changelog

Added

• Add support for a {SITE_ROOT_URL} placeholder in "default" preview client URL (#20) - Thanks @jaap3
• Add pre-commit support (#21) - @zerolab
• Add HeadlessMixin and HeadlessServeMixin (#22) - @zerolab based on code from @tbrlpld 🙌
• Add setting to redirect to the client preview URL (#23) - @zerolab based on real world code from @jaap3 🤘

Changed

• Move to GitHub Actions (#21)
• Update test targets, including Python 3.10 and Django 4.0 (#21)
• Move to a single, namespaced settings dictionary (#24) - @zerolab
• Updated repository structure for lighter packages (#25)