Integration Of A Rust Postgres Interval

[piperRyan]

Hey, a bit of a duplicate of #60 but I wanted to clarify a few points and poll a bit of use cases from the community. Namely, as part of my attempt to stabilize the interface for my project here, which is a dedicated interval type, I hoping to get the following things:

• Get some general feedback in terms overlooked use cases or use cases that could be stripped out of the project.
• Suggested strategy to integrate into this project namely would it be more preferable to do something comparable to how the chrono stuff was integrated or would it better to do something like postgres-array.

Thanks!

As a aside if you want me to move this to #60 I would be happy to, but I was thinking that would be more of when it does actually get integrated then close it kinda of deal.