Fix #1809: All-masked integer columns are written as <TD/>, even though
that violates the VOTable standard prior to version 1.3
Band-aid cyclical import problems that prevent running packages that
define Table types on their own in the test framework.
Add test for out-of-range null value
Fix regression test for io.votable.validate
Add CHANGES entry
Change to epoch_scale earlier for TimeFromEpoch; closes #1122
Add test cases, TimePlotDate correction
Merge pull request #1809 from mdboom/vo/empty-fields

How to use ``astropy.io.votable`` to fix non standard-compliant tables?
Add note to CHANGES.rst
Correction to plot_date doctest in docs/time/index.rst
Try changing empy lines in CHANGES.rst to get rid of
Reword CHANGES.rst to make more obvious to non-intimi what problem was fixed.
Merge pull request #1732 from mhvk/time-fromepoch-scale-conversion

Time fromepoch scale conversion (closes #1122); TimePlotDate correction
Refactor table Column code into a separate file
Merge pull request #1837 from taldcroft/table/factor-col

Refactor table Column code into a separate file