This module defines an abstract interface for database drivers in Julia.
This module contains abstract types, abstract required functions (which throw
a NotImplementedError by default), and abstract optional functions (which
throw a NotSupportedError by default).
Database drivers should import this module, subtype its types, and create methods for its functions which implement the signatures and behavioural specifications contained within this module.
This interface is largely inspired by Python's DB API 2.0, which is in the public domain: PEP0249.
All values of type T that could be null should be returned as
Nullable{T}.