0.12.0

• [Improvement] Add support for Prometheus as Backend. This allows to use Prometheus-compatible software as carbonapi's backends (e.x. Prometheus and VictoriaMetrics)
• [Improvement] Add support for querying msgpack-compatible backends. This should make carbonapi compatible with graphite-web 1.1 and grafana/metrictank
• [Breaking][Improvement] Integrate carbonzipper 1.0.0. This introduces better loadbalancing support, but significantly changes config file format. It might behave differently with the same settings. It also removes carbonzipper dependency.
• [Improvement] seriesByTag Support (thx. to Vladimir Kolobaev)
• [Improvement] aliasByTag Support (thx. to Vladimir Kolobaev)
• [Improvmenet] groupByTags Support
• [Improvement] Added support for more aggregation functions (thx. to Oleg Matrokhin)
• [Improvement] Add 'aggregate' function.
• [Improvement] pixelRatio for png render (thx. to Roman Lomonosov)
• [Fix] Supported functions were updated to be more compatible with graphtie-web 1.1.0+
• [Fix] fix movingXyz error on intervals greater than 30 days (thx. to Safronov Michail)
• [Fix] Fix timeShift function (thx. to Gunnar Þór Magnússon)
• [Breaking][Code] Migrate all internal structures to github.com/go-graphite/protocol/carbonapi_v3_pb. This removes redundant IsAbsent slice and changes all timestamps to int64 (they are still expected to have uint32 timestamps there)