Make native query in standalone Waterline

**Waterline version**: 0.13.3
**Node version**: 8.11.1
**NPM version**: 5.8.0
**Operating system**: Ubuntu 17.10

Hello!

When I trying to use Waterline in standalone mode, I could not find the correct method to perform native queries. With Sails.JS the sendNativeQuery method is used which I could not find in the instances of the models. Does anyone know how I can perform these queries?

Thank you!
`Waterline.start(waterlineConfig, function(err, orm) {
if (err) {
return console.error(err);
}

Waterline.getModel('User', orm).sendNativeQuery(sql);

console.log(orm);

});`

Start with the standalone Waterline.start callback and the Waterline.getModel('User', orm) call shown in the report; inspect how model instances expose native-query operations, using sendNativeQuery as the comparison point. Reproduce the missing method with the provided snippet and define done as a supported standalone path for native SQL, or clear documentation of the supported entry point.

Written by the indexing model from the issue text.