Py-ART version 1.7.0

Version 1.7.0 is the result of 7 months of work by 8 contributors.
Thanks to all contributors, especially those who have made their first
contribution to Py-ART.

Highlights of this release:

* Reading of Rainbow files.
* Reading of Argentinean H5 files.
* Optimized reading of NEXRAD Level II files.
* Better support for reading ODIM H5 and GAMIC files.
* Grids can be output to GeoTIFF files.
* Support for creating and reading horizontal wind profiles.
* Simulated radial velocities from a wind profile.
* Pseudo-PPIs from RHI volumes.
* Computation of secondary moments.
* Noise correction of RhoHV.
* Gatefilter based upon the texture of polarimetric variables.
* The region based dealiasing routine may use a wind profile for reference.
* Variational KDP retrievals.
* Routine for despeckle fields.
* Example showing how to overlay contours on radar plots.
* Various bug fixes and minor enhancements. 

Contributors to Py-ART 1.7.0:

Cory Weber 
Jonathan J. Helmus 
Jordi Figueras
Kai Muehlbauer
Kirk North 
Scott Collis
Steve Nesbitt
Timothy Lang 

The following have been deprecated and will be removed from Py-ART after
one additional point release (included in 1.8.0, removed in 1.9.0).

• The sounding_heights, sounding_wind_speeds, and sounding_wind_direction
  parameters of the pyart.correct.dealias_fourdd function. These parameters
  should now be specified in the sonde_profile argument.
• The pyart.correct.find_time_in_interp_sonde function. With the availability
  of the pyart.io.read_arm_sonde_vap function this function is no longer
  needed.