Added tests for new functionality (to be added).
Fixed typo.
Rough implementation of health check system

Tests fail, so not final.
Breaking up validate_broadcast to handle many bcasts.

This is done to test things like health check service recovery.
Such a recovery would have both a down and an up, so the state
progression and conresponding broadchast messages should be checked.
adding helthy service works
Removed unused tests.
Fixed typo
Further progress, but still unhealthy service no worky
Fixed unhealthy_service test
Much improved/useful health check: qc not passing still.

Doesn't play nicely with interweaved node up, service up, service down
and node downs yet.
heath tests full pass
Added documentation and specs.
Fixed warnings.
Added a spec.
Added tests for service_up/3
rewriting revised readme in .md and removing .org version.
Fixed typos and a mis-spec
Removed code duplication for service add/drop
Refactored health_fsm to make fsm part explicit
Health check is set in milliseconds now

Also using a macro to define default rather than a magic number