Added php project and its unit tests.

src/Simple.php

@@ -0,0 +1,16 @@
+<?php
+
+class Simple
+{
+    public function add($a, $b)
+    {
+        return $a + $b;
+    }
+
+    public function subtract($a, $b)
+    {
+        return $a - $b;
+    }
+}
+
+?>