feat: parser now writes, added missing fields

updated docs, example, extensive use of Traits with better handling.
valid level 9 phpstan codebase.

src/Traits/HasAuthority.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Ivuorinen\BusinessDataFetcher\Traits;
+
+trait HasAuthority
+{
+    /**
+     * @see getChangeString()
+     * @var int $authority What authority the change is related to.
+     */
+    public int $authority;
+
+    /**
+     * Get the name of the authority.
+     */
+    public function getAuthorityString(): string
+    {
+        return match ($this->authority) {
+            1 => 'Tax Administration',
+            2 => 'Finnish Patent and Registration Office',
+            3 => 'Population Register',
+            default => 'unknown:' . $this->authority,
+        };
+    }
+}