Feature/add period columns to queries

[LavenHook]

This PR may be a little premature. I have a need to be able to see the period columns when querying the complete history of an entity. Since the period columns are hard-coded* in this project, it seems fitting that the temporal table queries include the columns. *I think the period columns should be a little more flexible in the long run - which is something that I may consider working on myself, if/when I get time. This would also go hand-in-hand with issue #27 - add functionality to specify temporal table name and schema and #2 - Configure temporal column names.

For now, I offer this PR, which is enough to satisfy my simple use cases.

Thanks, Isaac