Allow plugins to handle raw embedded markdown content

[jhildenbiddle]

Feature request

See title.

Related:

• Docsify can not render an embedded  #1499
• After [filename](README.md ':include'), the docsify-tabs plugin in README.md fails #2000

Problem or desire

Plugins are unable to process embedded markdown content because docsify does not make this content available via a plugin's beforeEach hook. Instead, docsify retrieves the embedded markdown content, transforms it to HTML, and makes it available for the first time to a plugin via the afterEach hook. This prevents plugins like docsify-tabs from working with embedded content.

Proposal

See title.

Implementation

TBD