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

composer.json

@@ -0,0 +1,30 @@
+{
+    "name": "gullevek/dotenv",
+    "description": "Simple .env file processing and storing in _ENV array",
+    "keywords": [".env", "dotenv", "_ENV", "environment variables"],
+    "type": "library",
+    "license": "MIT",
+    "autoload": {
+        "psr-4": {
+            "gullevek\\dotEnv\\": "src/"
+        }
+    },
+    "authors": [
+        {
+            "name": "Clemens Schwaighofer",
+            "email": "gullevek@gullevek.org",
+            "homepage": "http://gullevek.org"
+        }
+    ],
+    "homepage": "https://github.com/gullevek/dotEnv",
+    "minimum-stability": "dev",
+    "require": {
+		"php": ">=7.4.0"
+	},
+    "archive": {
+        "exclude": ["/test/", "/test/*", "/phpstan.neon", "/psalm.xml", "/.phan/", "/.vscode/", "/phpunit.xml"]
+    },
+    "require-dev": {
+        "phpunit/phpunit": "^9"
+    }
+}