Install PHP code sniffer

PHP code sniffer is a linter for PHP. We will use this to do mass fixes to code style / code formatting.

- Install PHP code sniffer
- Upgrade phpunit
- Switch phpunit to a dev dependency

.phpcs.xml

@@ -0,0 +1,9 @@
+<ruleset>
+    <arg name="tab-width" value="4"/>
+    <exclude-pattern>/.github/</exclude-pattern>
+    <exclude-pattern>/.vscode/</exclude-pattern>
+    <exclude-pattern>/gitignore/</exclude-pattern>
+    <exclude-pattern>/screenshots/</exclude-pattern>
+    <exclude-pattern>/vendor/</exclude-pattern>
+    <rule ref="Squiz.WhiteSpace.SuperfluousWhitespace"/>  
+</ruleset>

composer.json

@@ -1,5 +1,6 @@
 {
-    "require": {
-        "phpunit/phpunit": "^9.5"
+    "require-dev": {
+        "phpunit/phpunit": "^9.5",
+        "squizlabs/php_codesniffer": "*"
     }
 }