Changes applied to PyArt to process airborne radar data,
specifically used NOAA P-3 Doppler radar data converted
using the NCAR Radx software package.
Merge remote-tracking branch 'arm_doe/master' into airborne

Allows the reading and displaying of cfradial airborne radar data.
Updated to test working order with lower fuselage data
Additional changes to Airborne RadarDisplay code to increase variables read in cfradial.

Added additional coordinate transformations.
Merge branch 'airborne'
MAINT: Sigmet extended headers can now be read.

This is in preparation for reading NOAA Hurrican Hunter Aircraft
tail radar data which has an extended Sigmet header.
STY: PEP8 and docstring clean of airborne code.
ENH: read_sigmet can read NOAA Hurrican hunter aircraft radar.
MAINT: time_ordering when reading sigmet file with extended headers
MAINT: refactor of _sigmet_noaa_hh module
ENH: radar.info prints airborne parameters
ENH: Default metadata for airborne parameters
MAINT: cleanup of coord_transform module
MAINT: clean up of radardisplay_airborne module
DOC: added airborne modules to developer reference manual
BUG: azimuth and elevation returned as degrees for airborne sigmet radar
Merge branch 'jjhelmus-airborne' into airborne

Merging with jjhelmus update of airborne part of code.
Merge pull request #180 from nguy/airborne

Airborne PyArt