Adding int4range type, and enabling Test-Kitchen-driven development

Adding the int4range type.

Also, given that epgsql requires a running postgres server with a very
specific configuration, and some specific test data pre-loaded, I've
integrated it with TK to make it easy to work on it.

Now running the test suite is as delightful as running `kitchen verify`!

Future work: put it on travis. Might do when I find some spare time.
The `check_type` fun is a bit weird, but basically : 
* the 1st arg is the type (obvious)
* the 2nd is a string to insert "as is" in a query, and it checks that it gets the 3rd back
* the 4th is a list of items, for which it checks that they support a round-trip : inserting them in the DB, then retrieving them, and checks it stays the same