extract [rfced] comments

[ajeanmahoney]

RPC staff ask questions to the authors by adding <!-- [rfced] --> comments to the document file. For example:

<!-- [rfced] Per our current process, please review the "Inclusive
Language" portion of the online Style Guide at
<https://www.rfc-editor.org/styleguide/part2/#inclusive_language>,
and let us know if any changes are needed.-->

These comments are currently extracted from the RFCXML via the get-comments2.py script and sent to stdout or redirected to a text file. In our current process, the RFC editor copies and pastes these comments into an email message to the authors at the beginning of AUTH48. For examples, see the auth48archive mailing list.

In this application, the user should be able to select "Extract [rfced] comments" from a menu or toolbar. The comments are then displayed in the order in which they appear in the XML or md in a new tab or window. The user can save the comments to a text file or copy/paste the contents elsewhere.

Note, we don't want to extract all the comments, which may include author comments or comments added by xml2rfc, just the ones identified with [rfced].