feat(content): pass document data to remark plugins

[farnabaz]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

This is a proposal PR to inject document data into remark plugins. Plugins may read/modify document data.

resolves #781

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes (if not applicable, please state why)

[atinux]

Could you add a small exemple in the docs regarding the remark plugins to understand the advantage of having the document data?

[farnabaz]

I add a simple plugin:

• it detects <authors> tag in content
• find the original file path
• fetch contributors of file form Github api
• inject data into document data and update tag

SandBox: https://codesandbox.io/s/suspicious-leavitt-ygg26?file=/example/utils/contributors.js
Result: https://ygg26.sse.codesandbox.io/authors

[atinux]

It looks great 😍

[pi0]

Neat!