v2. General cleanup: read through RFC and add missing features

[opoudjis]

v2. General cleanup: read through RFC and add missing features

[opoudjis]

Note: Made cref implementation what MMark specifies, but I think the mmark code is faulty: it ignores <!-- as unrecognised HTML .

[opoudjis]

MMark handling of references also appears buggy: XML references do not appear to be processed correctly.

[ronaldtse]

@opoudjis that's very strange. <!-- ... --> is working with my MMark that treats it as a comment.

XML references are also working for me in this way.

XML reference:

<reference anchor='ISO-8601-2004' target='https://www.iso.org/standard/40874.html'>
  <front>
    <title>ISO 8601:2004, Data elements and interchange formats --
    Information interchange -- Representation of dates and times</title>
    <author>
      <organization>International Organization for Standardization</organization>
      <address>
        <uri>http://www.iso.org</uri>
      </address>
    </author>
    <date month='December' year='2004'/>
  </front>
</reference>

Usage of reference

The format is based on the [ISO-8601-2004] duration representation...