fix(text): Update non-ASCII art text

[kesara]

Fixes #617

This change introduces two new command line options for text:

       --rfc-html-archive-url
          Default value: https://www.rfc-editor.org/rfc/
          URL for HTML file archive of RFCs.

       --id-html-archive-url
          Default value: https://www.ietf.org/archive/id/
          URL for HTML file archive Internet-Drafts.

Update text outputs:

For I-Ds:

(Artwork only available as svg: see https://www.ietf.org/archive/id/<docname>.html)

For RFCs:

(Artwork only available as svg: see https://www.rfc-editor.org/rfc/rfc<rfc number>.html)

[cabo]

Is it possible to link to the actual figure?

[kesara]

@cabo figure for artwork is optional. HTML processor adds anchors when there is no figure for artwork. HTML processing and text processing are two separate processors. It is hard to guess the HTML anchors by text processor accurately.