Introduce sidereal_time method to Time
Also changed internal use of lon, lat: swapped order in call sequence to
match convention (and coordinates), made default None, so that error can
be raised if an local sidereal time is requested, and used Longitude/Latitude
for them so that they can be defined much more easily.
Add documentation
Use explicit order arguments in format; proper spacing in CHANGES.rst
Formal sidereal_time.__doc__ such that build_sphinx is happy
Angle subclasses should decide on class; correct Latitude.__setitem__, doing
validation upfront and ensuring no temporary object is created
Add test case to ensure out-of-bounds setting of items doesn't corrupt input
Small adjustments to sidereal time documentation
Convert integers to float by default
Adjust tests to reflect that float is now default
Simplify can_cast test for numpy 1.5
Adjust __doc__; adjust comments in test for preservation of explicit dtype=int
Update examples in quantity.rst and note automatic conversion to float
Ensure that default dtype is np.float for quantity input as well
Update documentation and tests for float=default
Don't check dtype for copy=False, ensuring that that remains fast
Entry among API changes in CHANGES.rst
Remove DeprecationWarning superclass for AstropyDeprecationWarning

we do this because in py2.7, DeprecationWarning and subclasses are hidden by default, but we want astropy's deprecations to get shown by default
Add PR number to CHANGES.rst
Add PR number to CHANGES.rst
Rewrite use of _validate_angles in __setitem__ following @taldcroft's comment