Fix wiki navigation, update wiki changelog, improve documentation, and fix tests workflow

composer.json

@@ -14,9 +14,10 @@
         "php": ">=7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.5",
+        "phpunit/phpunit": "^7.5 || ^8.0 || ^9.0",
         "squizlabs/php_codesniffer": "^3.5",
-        "wp-coding-standards/wpcs": "^2.3"
+        "wp-coding-standards/wpcs": "^2.3",
+        "dealerdirect/phpcodesniffer-composer-installer": "^0.7.0"
     },
     "autoload": {
         "psr-4": {