Add getitem to MaskedColumn to copy attrs for slicing
Update CHANGES.rst [skip ci]
Add Table-level test of changing MaskedColumn attr and slicing
Slight performance enhancement for Const models.

See https://github.com/astropy/astropy/pull/3027#issuecomment-59576917
Moved column checking to before table instantiation
Moved single column check to actual reading
Merge pull request #3033 from embray/modeling/const-improvement

Slight performance enhancement for Const models
Merge pull request #2892 from mdmueller/improve-guessing

Made `_guess` avoid a couple cases in which Tables are instantiated and then ignored
Merge pull request #3023 from taldcroft/table-masked-col-3023

Rename masked column fails for subsequent slicing
Fix bug initializing from ndarray with multidim column
Update CHANGES.rst