Map Nagios exit codes
Renamed ExternalCommand to NagiosPlugin
Extracted Nagios parsing function
At some point, I'll actually work out how to parse the string best

(and stop procrastinating with scaffolding)
Rough proposal outline for "plugin"/"check"/"metric" support
Added note about Nagios plugin usage
Slightly more sensible Nagios parsing
Munin notes
More detail on standalone plugins
Moved Main -> Lux/Main
Skeleton tests
Vaguely improved Nagios spec
Merge branch 'feature/plugin_proposal' into develop
Merge branch 'feature/nagios_support' into develop