- Breaking internal API changes. See [v4 migration notes](https://github.com/markdown-it/markdown-it/blob/master/docs/4.0_migration.md). In usual case you will need to update plugins.
- Token internals changed
- Unified the most of renderer methods.
- Changed tokens creation - use `state.push(...)` (see sources)
- Moved `normalizeUrl()` to root class as `.normalizeLink()`&
added `normalizeLinkText()` method.
- Moved `.validateUrl()` to root class and simplified logic - no more need to
replace entities.
- Joined md unescape & replace entities logic to `utils.unescapeAll()`.
- `md.utils.lib` now exposes useful libs for plugins.
- Use entities data from external package.
- Fixed emphasis regression, caused by CM v0.18 spec (#65).