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/doctrine/instantiator/psalm.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0"?>
+<psalm
+    errorLevel="7"
+    phpVersion="8.1"
+    resolveFromConfigFile="true"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="https://getpsalm.org/schema/config"
+    xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
+>
+    <projectFiles>
+        <directory name="src" />
+        <ignoreFiles>
+            <directory name="vendor" />
+        </ignoreFiles>
+    </projectFiles>
+</psalm>