Use systemd management facilities

[No9]

As part of the discussion in #44 (comment) it was suggested that on systems using systemd the agent could open a socket directly to systemd-coredump via its socket (/run/systemd/coredump) and process the results. That would requires less kernel configuration and enable the collection from a container.

While this isn't an immediate requirement for any of our target platforms if someone was hesitant about deploying a binary onto a host or didn't wish to modify the kernel_pattern tunable this could be an option.

There is no plan to develop this as yet but PRs with this functionality will be accepted.
Just let us know you're starting so that others are aware the work is happening.

[No9]

Using systemd may also address the process management requirement that came out of this issue.
#86