added a pretty-print wrapper for coordinates
RA should print as hours if sexagesimal printing used
format -> to_string
completely changed coordinates.to_string to accept common style formats
allow empty style
test fixes & new tests
allow for vectorized units
apparently unicode strings are no longer returned...
import fix
unicodify & drop Coordinates from ICRSCoordinates (in tests)
typo in doctest
Fixed bug with Angle formatting
Tidy up SphericalCoordinatesBase.to_string, make defaults depend on coordinate system.
Fix failures with Python 3.2
Fix tuples with negative values in ``sexagesimal_to_string``
Added short description of ``to_string`` in the docs
Use parametrize for tests
Merge pull request #1296 from keflavich/coords_pprint

`.format` shortcut for coordinates