PostgreSQL: Date/Time functions and types

[Vlix]

I'm thinking of adding a module to the PostgreSQL part of Esqueleto that will handle as many of the functions and types from the Date/Time Functions and Operators section as I feel is doable for a first iteration. Probably name it something like Database.Esqueleto.PostgreSQL.DateTime

Thought I'd make an issue to discuss this addition. I'd probably leave the operators be, for now, because of the complexity of the possible type pairs.