Replace the use of marked with remark for doc/json generation

[rubys]

Summary: over time the node.js build process has outgrown marked and it's regular expression based processing model. See:

#21081 (comment)
#21081 (comment)
#21081 (comment)

It is time to replace it with something that involves a proper syntax tree which can be programmatically manipulated and from which artifacts like JSON can be confidently generated.

[Trott]

@rubys I believe you've completed this work and this issue can be closed. Am I mistaken?

[Trott]

This work has been completed for some time and marked is no longer used in tools/doc.