io.ascii LaTeX table writer: add tablealign to latexdict

fixes #1777
Fix Astropy intersphinx URL
Correct behaviour of inplace ufunc's for Quantities holding non-contiguous data
update CHANGES.rst
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
Add `translate_units` kwarg that can delegate down to `fix`.
Fix reporting of which CUNITn element was changed by unitfix
Fix error reporting in Wcsprm.to_header
Add list of supported projections to wcs docs
Reformat entry in Changes.rst
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