v0.16.0

This version adds localization (i18n). One entry holds the text of each
language of a multilingual website, and the editor shows one language at a
time. Editors and agents can find what still needs a translation.

Added

• Localized fields. A site declares its locales, defaultLocale and
  fallback, with the names of Astro's i18n. A field with localized: true
  stores a value for each locale in the same entry, and rich text has one file
  for each locale, such as body.de.mdoc. required applies to the default
  locale, and a missing translation never stops Save or Publish (ADR 42).
• localize(site, name, data, locale) in @micacms/astro gives an entry
  or a singleton in one locale. A missing value falls back to fallback, then
  to the default locale. localized: { fallback: false } keeps it empty.
• The locale in a page's URL. A url can name {locale}, such as
  /{locale}/news/{id}, with prefixDefaultLocale as in Astro. The preview,
  "Open on website" and the URL under the ID field show the page of the form's
  language, and the live preview's page changes the form's language. A
  localized id() must be unique in each locale: mica check and Publish
  report a duplicate (ADR 43).
• A language switcher in the header of a form, with the number of missing
  translations of each language. A button beside each localized field shows
  its other languages, can use one of them, and marks a missing translation.
• Find missing translations. The list of a collection shows the missing
  translations of each entry, and a filter shows the entries that miss one
  language. The Overview lists them for each language. The MCP tool
  list_entries gives missingTranslations and takes missing, and
  mica check lists them as information.
• localesOf(site, name, data) in @micacms/astro gives the locales that
  an entry has its own text in, for getStaticPaths, lists, the sitemap and
  hreflang (ADR 44).
• Links in rich text can get the address in the page's locale, with the
  link option of renderRichText.

Changed

• The header of a form is tidier: the status is below the title, and the
  entry's folder is below the form.
• A model with locales needs this version of Mica. Upgrade @micacms/editor
  and the image together with @micacms/astro. A site without locales writes
  the same .mica/schema.json as before.