Support for SIGHUP

[hholst80]

Closes #51

[hholst80]

This video was created by the patch. The video is correctly terminated when the terminal is closed.

screenrecord.mp4

[hholst80]

[I] root@trump ~/Code/wl-screenrec (signal-hup)
# cargo fmt --check -v
[bin (2021)] "/home/root/Code/wl-screenrec/src/main.rs"
[test (2021)] "/home/root/Code/wl-screenrec/tests/cmdline.rs"
rustfmt --edition 2021 --check /home/root/Code/wl-screenrec/src/main.rs /home/root/Code/wl-screenrec/tests/cmdline.rs
[I] root@trump ~/Code/wl-screenrec (signal-hup)
# git st
On branch signal-hup
Your branch is up to date with 'origin/signal-hup'.

nothing to commit, working tree clean
[I] root@trump ~/Code/wl-screenrec (signal-hup)
#