Add an option to show $comments in generated docs

[nicobo]

The "human views" of a JSON Schema may include "author" $comment fields on any object.
This may be used to document changes between 2 version or explain the exact purposes of fields for instance.

E.g.

"someObject": {
    "$comment": "This was changed into a string to allow internal references which are not an URI. Having an additional field was rejected because [...].",
    "type": "string",
}

Therefore it would be useful to display the value of $comment fields in the generated docs, possibly activated with a specific option.

[jkowalleck]

@dblanchette how do you feel about this feature? Is this something this tool should be capable of?