Default ``data_start`` to 0 in ``CommentedHeader``

fixes #2692
Made Latex/AASTex tables use unit attribute of Column for output
Provide np.broadcast_arrays replacement that allows subclasses
Determine whether to overload by testing for the actual problem
Add numpy license
Move from astropy.utils to astropy.utils.compat
Add documentation, and make things confirm to it
Do not import test function in compat.numpy; associated changes
Use final numpy version, use it in coordinates, add changelog entry
Only import what's necessary, slight modification of instructions.
Use importlib.machinery.all_suffixes if possible for open files test
Test for open files with travis
Support Python 2.6's lack of importlib

This change is made on a distro without python2.6 support, so good luck
Import importlib.machinery in open-files pytest plugin
Check for open files as part of all the base tests
quantity: remove space if unitless quantity
consolidate unitstr into property
fix doctests for dimensionless format call
add changelog entry
remove repr test