Show formatted dates as comments.

[bkuker]

I try to guess that a value is a Date:

• Numbers that look like seconds or millis between Jan 1 2000 and Jan 1 2038
• Strings that look like they came from JSON.stringify({'now': new Date()})
  and then include GMT and Locale formatted versions, as comments, in the formatted JSON.

I realize that the comment is not valid JSON, but it's not too far off, a user could likely still copy & paste the formatted output into most things.