Signal improvments

[creack]

Move signal to pkg + use strings instead of signal number to allow cross platform signal forwarding. An error is thrown in case of unknown signal.

[creack]

/cc @crosbymichael @vieux @unclejack @tianon

[vieux]

LGTM

[crosbymichael]

@creack DCO failed

[tianon]

+1 me gusta - now we don't have to hard-code the raw integer mappings for ourselves just for the client, and third-party clients will have an easier time using the signalling

[tianon]

Do those constants in "pkg/signal" (the syscall.* ones) map cleanly on other hosts? Or are you thinking about future non-Linux daemons way down the road there?

[creack]

@tianon It is a basic copy/paste from the syscall package from the different platform. So they map to their host.
I didn't think about non-linux daemon, but it should work fine. Small reserve on windows client though, but we'll see once we get there.

[creack]

@crosbymichael DCO fixed

[tianon]

cool, SGTM 👍

[crosbymichael]

LGTM