used latest stable release of cascading: 2.5.1
Merge pull request #218 from fs111/develop

used latest stable release of cascading: 2.5.1
Preserve order for grouping fields.
Make it even simpler.
Merge pull request #220 from funkenblatt/fix-grouping

Preserve order for grouping fields.
update codox ver to 0.6.6
Merge pull request #221 from Quantisan/develop

update codox ver to 0.6.6
CascalogTap should implement ISelectFields
Merge pull request #222 from sorenmacbeth/develop

CascalogTap should implement ISelectFields
fixes #217
Merge pull request #223 from sorenmacbeth/develop

fixes #217
Remove duplicate import in operations.clj
Merge pull request #225 from ajtulloch/patch-1

Remove duplicate import in operations.clj