Modify SpanGroup to support millisecond timestamps
Modify SpanGroup to support millisecond timestamps

Signed-off-by: Chris Larsen <83037b211e1d109d6858769a113e269c3139ffd3@euphoriaaudio.com>

MadDogTechnology/opentsdb,MadDogTechnology/opentsdb,alienth/opentsdb,johann8384/opentsdb,ShefronYudy/opentsdb,OpenTSDB/opentsdb,OpenTSDB/opentsdb,eswdd/opentsdb,ShefronYudy/opentsdb,andyflury/opentsdb,andyflury/opentsdb,MadDogTechnology/opentsdb,johann8384/opentsdb,OpenTSDB/opentsdb,eswdd/opentsdb,alienth/opentsdb