Postfix redesign

Now there are three images tags for `postfix`. `:latest` uses encryption
and authentication for inbound and outbound mail. It listens on posts 25
and 465. Because it authenticates, I dropped the requirement for
senders to have a LAN IP.

`:tls-in` drops outbound encryption and authentication. This is
generally going to be useful for receiving mail and handing it to a
local service.

`:tls-out` drops inbound encryption and authentication and listining on
port 465. This is useful for relaying mail off of a trusted host.

Added apkbuilder

Minor adjustments to documentation

sr.ht

Adding a postfix server image.

Adding images for the sr.ht system (meta+todo+git).

Updates

Added a main README file to act as a directory.

Updated nitter Makefile.

Added useful base images (fcgi and php).