Bring MyST document engine up to feature parity with Jupyter Book, with the intent of offering MyST as a backend to Jupyter Book

[choldgraf]

Goal

Jupyter Book users should be able to utilize the new MyST document engine with no significant degradation in functionality or UX.

Outcome and measures

• Most users of Jupyter Book can use the MyST build engine without any errors with less than 30 minutes of conversion work.
• Key Jupyter Book user communities report no blocking problems with the MyST build engine

Reference

List of feature comparisons here:

• Audit of Features missing in JupyterBook #189

Initiatives

• Launch the MyST -> Jupyter Book parity project #1001
• Minimum Viable Product of Jupyter Book functionality with MyST #1106