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/phpunit/php-invoker/composer.json

@@ -0,0 +1,54 @@
+{
+    "name": "phpunit/php-invoker",
+    "description": "Invoke callables with a timeout",
+    "type": "library",
+    "keywords": [
+        "process"
+    ],
+    "homepage": "https://github.com/sebastianbergmann/php-invoker/",
+    "license": "BSD-3-Clause",
+    "authors": [
+        {
+            "name": "Sebastian Bergmann",
+            "email": "sebastian@phpunit.de",
+            "role": "lead"
+        }
+    ],
+    "support": {
+        "issues": "https://github.com/sebastianbergmann/php-invoker/issues"
+    },
+    "prefer-stable": true,
+    "config": {
+        "platform": {
+            "php": "7.3.0"
+        },
+        "optimize-autoloader": true,
+        "sort-packages": true
+    },
+    "require": {
+        "php": ">=7.3"
+    },
+    "require-dev": {
+        "ext-pcntl": "*",
+        "phpunit/phpunit": "^9.3"
+    },
+    "autoload": {
+        "classmap": [
+            "src/"
+        ]
+    },
+    "autoload-dev": {
+        "classmap": [
+            "tests/_fixture/"
+        ]
+    },
+    "suggest": {
+        "ext-pcntl": "*"
+    },
+    "extra": {
+        "branch-alias": {
+            "dev-master": "3.1-dev"
+        }
+    }
+}
+