Add support for Teradata's QUALIFY clause

[slessard]

This PR is a replacement for #344. This PR contains all the same code changes as #344 but without all the noise of the module name change.

This change adds the feature requested in #343. This PR adds support for the QUALIFY clause found in Teradata SQL dialect. The feature is off by default. I wrote some unit tests and even tested it against a Teradata database.