logind: Set session type from env
logind: Remove session type check
logind: Remove useless check
meson: Set license to MIT
seatd: Use path-based chmod/chown

The fd variants do not seem to work for sockets
ci: Install scdoc for alpine and archlinux
man: Add simple seatd(1) page
build: check for libelogind before libsystemd

elogind provides a libsystemd wrapper which is packaged by some distros.
For whatever reason using this wrapper instead of libelogind directly
causes compiler warnings to pop up. Checking for libelogind first
ensures that this wrapper is not used.
contrib: Add example systemd service
seatd: Add command-line arguments
ci: Run unittests on all platforms
linked_list: Add unittest
logind: Allow SwitchTo for all seats
logind: close_device always returned error

Error handling was broken in close_device, always returning -1.

Use the return value, and add a few errno assignments while we're at it.
libseat: Fix doc typo
libseat: Rename libseat_impl to seat_impl
log: Remove libseat prefixes
Remove pointless compiler.h
linked_list: Assert initialized list in linked_list_empty
seat: Fix device double-remove
seatd: Unlink default seatd socket on startup