Add PostgreSQL Support (#3)

Reviewed-on: #3

src/DocumentIndex.php

@@ -0,0 +1,15 @@
+<?php declare(strict_types=1);
+
+namespace BitBadger\PDODocument;
+
+/**
+ * The type of index to generate for the document
+ */
+enum DocumentIndex
+{
+    /** A GIN index with standard operations (all operators supported) */
+    case Full;
+
+    /** A GIN index with JSONPath operations (optimized for @>, @?, @@ operators) */
+    case Optimized;
+}