Fix create_table call

We weren't passing that up the chain, causing much wailing and gnashing of
teeth.

Much improved API *and* implementation

Based on feedback from Jeremy Evans, I've done some work on the
implementation (to make it safer and simpler), which has necessitated some
definite improvements to the API itself. Hopefully nobody was deeply
married to the old version.

Initial commit

In theory, this release should allow the creation of comments on
all PgSQL object types, from any method within Sequel that creates a new
object.

In theory.