olddoc 1.7.0 - Earth day!

Since most users are on horrible GUI browsers which default
to light backgrounds, implement the "dark216" color scheme
which saves power on OLED and CRT displays.  This still
respects "prefers-color-scheme:light" on newer browsers,
so users can burn their eyes out if they wish :P

While we're at it, switch to perlpod for our own documentation
since Perl5 and POD tooling is more common on most *nix systems
than pandoc.  Finally, update our documentation to avoid the
term "mailing list" because centralized subscriber lists limit
forkability compared to an "archives first" approach to email.

3 changes since v1.6.0 (2019-01-07):
  add dark216 color scheme for power savings
  doc: switch to perlpod for documentation
  doc: update wording to avoid "mailing list"