transition to a simple txt-based setup, plus txt2html

manually maintaining four different versions of my notes (plain text,
html, atom, and rss) turned out to be a bit much.  and i don't
particularly enjoy hand-writing the latter three anyway.

as such, i'm now moving to a barebones setup where everything is
written in plain text, and a simple script like txt2html (shout out to
public-inbox and Eric!) is used to add convert to html with minimal
changes, such as linkifying URLs -- aside: it beats me why so called
"modern browsers" don't already do this out of the box for txt files.