Added inverse to some models and SCompositeModel.
Make it easier to subclass Table

Before this patch, every subclass needed to implemented its own
_new_from_slice.
add more tests, replace other hardwired Table
Removed  flag and clarified error message
Merge pull request #1199 from nden/add-inverse

Added inverse to some models and SCompositeModel.
Merge pull request #1142 from hamogu/subclasstable

Make it easier to subclass Table
Make Astropy logo linkable and redirect user to Astropy.org.
Added table.copy() method. Closes #965
Fix for issue #696
Merge pull request #1209 from gabraganca/master

Close #1157 : Make the Astropy logo linkable.
Merge pull request #1208 from ChrisBeaumont/table_copy

Added table.copy() method. Closes #965
Merge pull request #1213 from ehogan/fix-issue-696

Fix for issue #696