Influxdb: Part 1

This is the first PR to fix #39. It is not fully implemented, the ``Percentiles()`` method is missing now. For others, they have already passed the unit test.

Because of influxdb/influxdb-go#12, we are unable to enable compression. But we could enable it once influxdb/influxdb-go#12 get fixed.

I did not change .travis.yml, because we need to do some installation on the CI's container. I leave it as another PR.
I'm not familiar with influxdb, but is this what they'd expect? a point per stat, or they'd rather have them all in one point?