Class rename, composer add, phpUnit tests add

Rename the class from ReadEnvFile to DotEnv.
Add everything to a composer json file so it can be published to
composer repository.
Add phpUnit tests for system

vendor/nikic/php-parser/lib/PhpParser/Internal/DiffElem.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\Internal;
+
+/**
+ * @internal
+ */
+class DiffElem
+{
+    const TYPE_KEEP = 0;
+    const TYPE_REMOVE = 1;
+    const TYPE_ADD = 2;
+    const TYPE_REPLACE = 3;
+
+    /** @var int One of the TYPE_* constants */
+    public $type;
+    /** @var mixed Is null for add operations */
+    public $old;
+    /** @var mixed Is null for remove operations */
+    public $new;
+
+    public function __construct(int $type, $old, $new) {
+        $this->type = $type;
+        $this->old = $old;
+        $this->new = $new;
+    }
+}