Add types declaration file (resolve #46)

index.d.ts

@@ -0,0 +1,28 @@
+declare module 'objection-hashid' {
+  import { Model } from 'objection-2';
+  import { QueryBuilder } from 'knex';
+
+  class HashIdExtensionClass extends Model {
+    static get hashIdSalt(): string;
+
+    static get hashIdMinLength(): number | void;
+
+    static get hashIdAlphabet(): string | void;
+
+    static get hashIdSeps(): string | void;
+
+    static get _hashIdInstance(): string;
+
+    get hashId(): string;
+
+    get hashid(): string;
+
+    static get hashIdField(): string;
+
+    static get hashedFields(): Array<any>;
+
+    $formatJson(obj: object): object;
+  }
+
+  export default function (model: new (...args: any[]) => Model): new (...args: any[]) => HashIdExtensionClass;
+}