Update documentation and finalize release 1.2.

Support converting Markdown into a string without any markup.

Cleaned up Package.swift. Updated CHANGELOG.

Remove debug output.

Adjust project to Xcode 14.3.

Force usage of URL syntax in `AttributedStringGenerator`.

Allow customization of image sizes in the `AttributedStringGenerator`…

…. Support relative image links in the `AttributedStringGenerator`.

Encode predefined XML entities also for code blocks in HTML generator.

Fix accessibility bug. Update change log.

Allow construction of Definition objects outside of MarkdownKit.