Better E2 Documentation/Helper

[Denneisk]

Use an in-house or third-party documentation tool to generate better E2 documentation that can annotate a little better than what we have currently (or at least a little prettier than current e2docs).

See also: #2474 (comment)

And maybe also have an automated action to update documentation.

Could have the client generate documentation on opening the helper. The client could request a small amount of function signatures to check if the server has them, and if they're not enabled, to grey/strike them out. Could be unreliable and the client requests only as needed.

Distantly related to #2759; using the same annotation for e2functions and docs just makes sense.