added test_imports to make sure all packages successfully import
initial structure of coordinates subpackage
Added coords_example.py

This file should be removed once the examples have been converted to the
testing framework
added coordinates modules
updated example for changes in gist
converted coords_example to tests
moved Angle import into individual tests
added coordinates documentation to doc index
to_string -> format
updated to new astropy.units
More work on core, updated several tests.
New work on core, etc.
More work on Angle, RA classes. Improved __eq__ on Angle.
Typos.
Work on RA, Angle operators, test code.
Added more tests, new conversion routines, to_string handling.
Typos, tabs.
Starting work on "Coordinates", expanded custom errors, bug fixes.
Further development on Coordinates.
More work on coordinates classes, new tests.