mail/rss2email3: Update to 3.11

• This update unbreaks the port at runtime by using the builtin "html.unescape()" function (introduced in Python 3.4) instead of the "html2text.unescape()" function from textproc/py-text2html which was removed since the 2019.8.11 release.

• Submitter becomes maintainer because the previous maintainer seems to be missing in action as there was no feedback over five months.

While I'm here:

• Switch manpages to the preferred share/man location.
• Remove no longer required CONFLICTS_INSTALL entry.
• Update the WWW field to point to the new upstream repository.

Changelog since 3.9:

https://github.com/rss2email/rss2email/blob/v3.11/CHANGELOG

PR: 243515
Submitted by: Corey Halpin <chalpin@cs.wisc.edu> (based on)
Reported by: Michael Bueker <m.bueker@berlin.de>
Approved by: maintainer timeout (5+ months)
MFH: 2020Q3 (blanket: runtime fix)