Add To/FromField for (Double, Double), point type

[avieth]

Tested and working with PostgreSQL 9.4.1.

[lpsmith]

Have you seen #154?

In particular, I won't accept a patch with (Double,Double) as the Haskell type. Other than that, it looks good to me.

Perhaps we could introduce a Database.PostgreSQL.Simple.Geometry module, and declare a data Point = Point {-# UNPACK #-} !Double {-# UNPACK #-} !Double type in there, with appropriate Haskell and postgresql-simple instances.

[avieth]

Your suggestion sounds good. Implemented in 4c37db1

[lpsmith]

Ok, now I'd move the ToField/FromField instances into the Geometry module as well, as that's more in keeping with similar such modules. Also, I really don't see any reason why the Point type should be abstract, I'd just go ahead and export the constructor. And I would add a few Haskell instances for Point, at the very least I'd add Eq and Typeable.

[avieth]

You're the boss :) latest commit moves To/FromField into Geometry.hs and exports Point.