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/Node/Expr/AssignOp.php

@@ -0,0 +1,30 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\Node\Expr;
+
+use PhpParser\Node\Expr;
+
+abstract class AssignOp extends Expr
+{
+    /** @var Expr Variable */
+    public $var;
+    /** @var Expr Expression */
+    public $expr;
+
+    /**
+     * Constructs a compound assignment operation node.
+     *
+     * @param Expr  $var        Variable
+     * @param Expr  $expr       Expression
+     * @param array $attributes Additional attributes
+     */
+    public function __construct(Expr $var, Expr $expr, array $attributes = []) {
+        $this->attributes = $attributes;
+        $this->var = $var;
+        $this->expr = $expr;
+    }
+
+    public function getSubNodeNames() : array {
+        return ['var', 'expr'];
+    }
+}