refs https://github.com/TryGhost/Toolbox/issues/174
- this exposes `isMySQL` and `isSQLite` functions which can be used
within Ghost to figure out which DB we are using
- also cleans up public properties of the class
refs https://github.com/TryGhost/Toolbox/issues/175
- this library is a small utility around `knex` that returns info on the
database used - particularly, the version used
- this will initially be used within Ghost but it can be extended to
other databases and projects if needed
