better pickle support, various fixes and better aggregators

• support pickle protocol versions 0, 1, 2, 3 & 4 + accept pickle arrays + send pickle tuples. #341
• fix different connections to same host:port using same spool file, by adding instance to destination key. #349
• fix aggregator flush timing + limit concurrent aggregator flushing #354
• support new tsdbgw response with detailed info about invalid metrics #338
• add 'count' aggregator. #355
• Some aggregator improvements and better stats. #361, specifically:
  • assure aggregation flushing is in timestamp asc order
  • new stat for number of metrics going into aggregator: service_is_carbon-relay-ng.instance_is_$instance.mtype_is_counter.unit_is_Metric.direction_is_in.aggregator_is_$aggregator
  • new stat for number of metrics going out of aggregator: service_is_carbon-relay-ng.instance_is_$instance.mtype_is_counter.unit_is_Metric.direction_is_out.aggregator_is_$aggregator
  • new stat for number of aggregators waiting to flush: service_is_carbon-relay-ng.instance_is_$instance.*.unit_is_aggregator.what_is_flush_waiting
  • new stats for CPU, memory and golang GC under `carbon-relay-ng.stats.$instance.*
  • give aggregators a "key" property for use in stats ($aggregator above), printed at startup and in web ui.
  • process pending aggregations more eagerly - instead of waiting - when relay is somewhat loaded.
• Fix bad regex cache clean up resulting in unbounded growth #365
• Fix deadlock in keepSafe #369
• Embed bootstrap, jquery, etc, instead of pulling in from the internet. #371