fix some -Wunused-const-variable warnings

Build ragel machines with 'nofinal'
reorganize headers
initial work towards supporting multiple agents

This is the easy work done. Problem is in reworking the cgroup
hierarchy. Work toward issue #21.
properly support multiple agents per user

Closes #21. Changes the monitoring scope to something along the lines
of 'envoy-ssh-agent-1000.scope'
Merge branch 'multiple-agents'

* multiple-agents:
  properly support multiple agents per user
  initial work towards supporting multiple agents
make internal variable and structure naming more consistent