Migrate from signal to sigaction

[OleStrohm]

According to the man page for signal(2) it's use is discouraged in favour of sigaction(2). Migration is very easy (Just make two sigactions, one for expire and for ignore. I've already tested this on my fork and it's quite easy. This is not crucial as signal(2) obviously works, but I think it's always good to try and use more up to date apis.

[dudik]

This was a great suggestion. The transition took a little bit more time than I expected, but everything should now work properly. Again, I might have forgot to test some odd edge case, so any testing on your side is appreciated. Thanks.

[OleStrohm]

LGTM!