refs https://github.com/TryGhost/Toolbox/issues/174
- ok, iteration 3 on how this library should work
- 95% of my use cases just need to pass an knex instance and return if
it's mysql/sqlite
- i don't want to have to initialize the class in this library to get
that
- this commit reworks the public interface to return a function with
some simple `is*` functions for those uses cases, or to return the
class otherwise
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
