Airborne PyArt 

The following modifications were made to Pyart:

pyart.io.cfradial

Added the following optional variables in the read_cfradial function:
rotation
tilt
roll
drift
heading
pitch
georef_applied

These variables are standard output when converting using the RadxConvert package.

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pyart.io.radar

The above variables were also added to the Radar class.  I did not add to info function,
as I thought this might be a developer decision.  Especially since these are specific 
to have a airborne (mobile) platform.

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Created pyart.graph.radardisplay_airborne

I created a new display class given the airborne radar unique geometry.

All sweep references were removed given each cfradial is a sweep file.  Hope this 
doesn't come back to haunt later versions.

I modified the plot_range_rings and plot_range_ring modules to allow the user to 
select linestyle and color.

I added a module plot_grid_lines to add grid lines if user desires.
The aspect ratio is important for decent figure so I added the call
ax.axis('scaled')
to the code

plot_colorbar is no longer an object
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Created pyart.graph.coord_transform

Needed for coordinate transformations, which differ than standard ground-based.
It is common-place to use the projection onto track-relative coordinates, but I included
a couple of other transformations that could be used and may be useful for other mobile
platforms.