Add todo.sr.ht webhooks service

Add todo.sr.ht-lmtp

todo.sr.ht: fix gunicorn invocation in init script

todo.sr.ht: normalize init scripts

Add -openrc, fix sources for todo.sr.ht

Update man.sr.ht.post-upgrade

Also moves alembic dependency to py3-srht

Tweaks to the todo.sr.ht package

Initial pass on todo.sr.ht package