check and flush frames while streaming points for a series
check and flush frames while streaming points for a series

TODO(sgc): implement `writer` type that handles all the details
of writing frames to the RPC stream. Additional responsibilities
of writer include

* point frame recycling to reduce memory pressure
* skip empty point frames
* skip series frames with no points

benbjohnson/influxdb,linearb/influxdb,nooproblem/influxdb,vladlopes/influxdb,mark-rushakoff/influxdb,linearb/influxdb,benbjohnson/influxdb,vladlopes/influxdb,influxdb/influxdb,vladlopes/influxdb,nooproblem/influxdb,influxdata/influxdb,influxdb/influxdb,influxdb/influxdb,benbjohnson/influxdb,mark-rushakoff/influxdb,nooproblem/influxdb,linearb/influxdb,influxdb/influxdb,benbjohnson/influxdb,mark-rushakoff/influxdb,influxdb/influxdb,mark-rushakoff/influxdb,mark-rushakoff/influxdb,influxdata/influxdb,linearb/influxdb,li-ang/influxdb,nooproblem/influxdb,linearb/influxdb,nooproblem/influxdb,mark-rushakoff/influxdb,vladlopes/influxdb,li-ang/influxdb,influxdb/influxdb