Add PostgreSQL Support (#3)

Reviewed-on: #3

src/Definition.php

@@ -31,4 +31,16 @@ class Definition
     {
         Custom::nonQuery(Query\Definition::ensureIndexOn($tableName, $indexName, $fields), []);
     }
+
+    /**
+     * Create a full-document index on a table (PostgreSQL only)
+     *
+     * @param string $tableName The name of the table on which the document index should be created
+     * @param DocumentIndex $indexType The type of document index to create
+     * @throws DocumentException If the database mode is not PostgreSQL or if an error occurs creating the index
+     */
+    public static function ensureDocumentIndex(string $tableName, DocumentIndex $indexType): void
+    {
+        Custom::nonQuery(Query\Definition::ensureDocumentIndexOn($tableName, $indexType), []);
+    }
 }