Shrink Public API Surface for 1.0 (Umbrella Ticket)

[jenshalm]

The major (or even sole) focus for 1.0.0-M2 will be to dramatically shrink the public API surface to ensure longterm binary-compatibility is feasible for the 1.x lifespan.

Many APIs are public "by accident", since it is the default access and earlier years did not put a major emphasis on bincompat anyway (it was an unrealistic goal as long as very large new sets of functionality were introduced). By now Laika has matured in a way that it makes sense to address these historic issues now.

The main public APIs that need to remain are:

• The core APIs to configure and run a transformation.
• The main extension APIs (everything reachable from the ExtensionBundle type).
• The theme support and Helium configuration and types reachable from there.
• The APIs of the included micro-libs, mainly parser combinators and config/hocon support.
• The API entry point to launch a preview server.
• The keys for settings and tasks in the sbt plugin as well as relevant helpers.

For everything else package-private should become the new default.

This will most likely leave behind some skeleton packages with only a few public types left. These will be "re-homed" later, but renaming and repackaging in general is left for the final milestone to keep the 0.19 maintenance branch largely in sync as long as possible.

To avoid a mega-PR the work will be split into the following sub-tasks (PRs will be linked here as soon as they are created):

• Core APIs & Utilities - shrink public API surface - core APIs #457
  packages laika.api, laika.ast, laika.format, laika.factory, laika.time, laika.collection
• Core Extension Points - shrink public API surface - core extension points #462
  packages laika.bundle, laika.directive, laika.parse.directive
• Hocon Config - shrink public API surface - config API & Hocon parser #463
  packages laika.config, laika.parse.hocon
• Parser Library - shrink public API surface in core parser library #473
  packages laika.parse, laika.parse.combinator, laika.parse.text, laika.parse.markup
• Core Internal Runtime - shrink public API surface in core runtime #474
  package laika.rewrite, laika.render
• Markup Parsers - Markdown & reStrucutredText - shrink public API surface in markup parsers #475
  packages laika.markdown, laika.rst
• Other Parser Implementations - shrink public API surface in syntax highlighter & parsers for CSS + URI #469
  packages laika.parse.code, laika.parse.css, laika.parse.uri
• laika-io User APIs & Runtime - shrink public API surface in laika.io.* #465
  package laika.io
• Theme Support & Helium Config - shrink public API surface in laika.theme + laika.helium #466
  packages laika.helium, laika.theme
• EPUB & PDF Renderer - shrink public API surface in EPUB and PDF renderer #468
  packages laika.render.epub, laika.render.pdf
• Sbt Plugin & Preview Server - shrink public API surface in sbt plugin and preview server #467
  packages laika.sbt, laika.preview