Merge branch 'master' into max-data-points
Consolidate datapoints (avg, sum, max, min)
Set null value for consolidation range with no datapoints

Setting 0.0 as a value for empty data points is not good approach. Null
values are compatible with graphite's json API.
Update README
Fix for Giraffe's Uncaught TypeError: Cannot set property 'data' of undefined

to be compatible with graphite  even if there is no data points
response array populated by nulls
Merge branch 'consolidate-datapoints_pr/2'

Conflicts:
	.gitignore
	README.md
	pkg/metrics/api.go
	pkg/metrics/metrics.go
	webserver/render/render.go
Update spin script

Use start-stop-daemon instead of '&'