WIP db api idea

Note: this is branched off #8.

The `.Sql()` `Task` extension would look for a .sql file (maybe as an embedded resource) in a location defined by a convention of having the same name as the corresponding `Task` with `.Tasks.` in the namespace replaced by `.Sql.`

`GetOne` and `GetMany` would be replaced with `Get` that works like `GetMany` did. The user can then choose to call .Single() or whatever.