Fixing documentation links, warnings in wcs
Fixing documentation links, warnings, PEP8 in stat, config, constants
Fixing documentation links, warnings, PEP8 in vo
Fix small typo
Support writing IPAC-style tables that contain no data

This fixes the following error:

    >>> import astropy.table
    >>> t = astropy.table.Table(names=['a', 'b'])
    >>> t.write('test.dat', format='ascii.ipac')
    ValueError: max() arg is an empty sequence
Add test for no-frame SkyCoord repr
Use NoFrame for SkyCoord with no specified frame
Expunge frame_name attribute in favor of frame.name
Escape backslashes in expected output
Added preferred_attr_units to NoFrame and reverted test changes that it makes unnecessary

at @taldcroft's suggestion
Merge pull request #2500 from eteq/fix-2486-take2

Alternative fix for showing "no frame" in SkyCoord
Merge pull request #2476 from bsipocz/fix_various_docs_links

Fix various docs links
Merge pull request #2498 from lpsinger/write_no_data_ipac

Support writing IPAC-style tables that contain no data