Add a new entry point: Start which takes configuration

[ramr]

Adds a new entry point called Start that takes a configuration. The old Reap stuff still runs as it did for backwards compatibility and in most cases, you shouldn't need to use Start. But if you want to push down config to wait4/waitpid, you can use the start entry point.

Usage:

import reaper "github.com/ramr/go-reaper"
...
config := reaper.Config{Pid: 0, Options: 0}
go reaper.Start(config)
...