ENH/API: Table.data can now take `dense`
DOC: added example to Table.data
MAINT: simplified Table.iter
ENH/API: added Table.iter_pairwise
DOC: updates to changelog
STY: pep8...
STY: moved iter_ construction, thanks @teravest\!
Merge pull request #483 from wasade/pairwise_iter

Merging as @teravest indicated this was good to merge