Fix lock services not stopping after waking up

Run in session.slice

From systemd.special(7):

> session.slice
>   All essential services and applications required for the session should use
>   this slice. These are services that either cannot be restarted easily or where
>   latency issues may affect the interactivity of the system and applications.
>   This includes the display server, screen readers and other services such as
>   DBus or XDG portals. Such services should be configured to be part of this
>   slice by adding Slice=session.slice to their unit files.

Include a changelog

Improve the README

Fix bogus log message

Translate session unlock event to unlock.target

Improve the README a bit more

Tidy up makefile

Notify systemd when we've initialised successfully

Use go-systemd for service management

Make logging format systemd-friendly

Improve error handling and logging

Tidy up infinite loop

Configure pre-commit hooks

Run linting and tests in CI

Readme tweaks

Update README

Some wording improvements and convert it to markdown.

Update project URL in service file

Update build instructions

Fix mixup in Makefile