metrics

Things we want

• labels: registry and metric level
• FAST (avoid locking where possible)
• interfaces -* make it easy for people to implement their own metric type
• namespaced metrics (something like a registry)
• pluggable (use with graphite, prom, etc.)
• register AND unregister metrics

Types of metrics

• counter
• gauge
• run func X to get the value: useful for things like "time since start"