rename SetOpen, to SetOpenFunc to follow naming conventions of other function stubs
refactoring interface so that methods are exposed on the package level, so that implementors don't need to setup the driver/connection etc, a simple Reset() method can serve the same purpose it's been used for
refactor so that internally used types are not exported, so that godoc's are not misleading, some of these could possibly be exposed later as go-testdb has more features, but for now they are only used to match interfaces so that it can mimic a proper driver within go's sql package
updating README to reflect new interface