* Fixed failing tags match in get_points() on a ResultSet:
    - This is a breaking change. Older influxdb servers that
      do not return tags as fields are not compatible with
      this change. This would result in the get_points()
      filters no longer working.
* Added pool size parameter to client constructor
* Added ping method to the client.
* Added support for not including all fields when using
  the series helper.
* Fixed typo in Content-Type header.
* Data arg in write() can now be a single string.
* Added method close to InfluxDBClient class.
* Added chunked query support for DataFrameClient.