2.18.0 * Fix the idType so that it works with both MongoDB and RDBs (Raymond Feng) * Tidy up tests so that they will work with RDBs (Raymond Feng) * Fix JS style issues (Raymond Feng) * Add a new property option `defaultFn` (Miroslav Bajtoš) * Fix the null/undefined check (Raymond Feng) * Fix createdAt type so that it won't overflow SQL server int (Raymond Feng) * ModelBaseClass: promise mode for notifyObserversOf (Miroslav Bajtoš) * ModelBaseClass: support promise-based observers (Miroslav Bajtoš) * use lodash to update the findBelongsTo which now returns an array of matches (Bryan Clark) * Add $now as shortcut default value for date property (Pradnya Baviskar) * Fix `deleteById(id)` and other test failures (Miroslav Bajtoš)