`twitfetch.py` fetches the threads defined in `tweets.txt`, and
then the tmux.html has an example (will likely be made a macro
in the future)...

[1] https://validator.w3.org/feed/

The issue is that w/ mark'd sections, the anchors will be relative
to the imported doc and NOT the source document..  So the markdown
toc feature that adds anchors to header tags would create permanent
links that won't work in the long term.  This fixes them up.

time, but only a date...  Time can be added once I figure out how
to handle timezones...  Always displaying in UTC doesn't make too
much sense, so maybe need to show the timezone as well...