MAINT: Created aux_io namespace, moved read_gamic.
MAINT: Radar and Grid objects moved to core namespace.

Closes #165
TST: Doc building is hushed when not in ARM-DOE repo.
TST: removed aux_io from coverage report.

This will increase the total coverage of the code since modules in
pyart/aux_io are excluded from the statement count.  Since these modules
explicitly state they may not be tested this seems reasonable.
Merge pull request #169 from jjhelmus/aux_io

MAINT: pyart.aux_io and pyart.core name spaces created.