Derive mode from DSN function

- Add headers in all files
- Minor field name changes

src/Op.php

@@ -1,4 +1,10 @@
-<?php declare(strict_types=1);
+<?php
+/**
+ * @author Daniel J. Summers <daniel@bitbadger.solutions>
+ * @license MIT
+ */
+
+declare(strict_types=1);
 
 namespace BitBadger\PDODocument;
 
@@ -27,11 +33,11 @@ enum Op
     case NEX;
 
     /**
-     * Get the string representation of this operator
+     * Get the SQL representation of this operator
      *
      * @return string The operator to use in SQL statements
      */
-    public function toString(): string
+    public function toSQL(): string
     {
         return match ($this) {
             Op::EQ  => "=",