Extract an interface from the Consul class

[StuporHero]

I'd like to be able to delegate to the Consul class so I can create a ValidatedConsul class in my own project that lets me inject my own custom validations into its methods without having to sprinkle validation code through my entire project. Ideally, Consul would be the name of the Interface and DefaultConsul or ConcreteConsul would be the class name, which would be a breaking change requiring a major version bump, but adding an IConsul Interface and replacing all internal uses of Consul with it would let you bump the minor version instead and not break things for everyone.