Add PHP8

- update README.md with latest PHP information
- update composer.json to support PHP 7.3 to PHP8
  - active support for PHP 7.2 ended 6 Dec 2020
  - PHP8 was released 26-Nov-2020
  - update the dependencies
- PHPUnit now version 9.5 and config file updated
- ECS now version 9.3 and config file changed from `ecs.yaml` to `ecs.php`

ApprovalTest removed, in line with latest readme, all set for refactoring :)

Tested with PHP 7.3, 7.4 and 8.0 one failing "fixme" != "foo" test!

php/ecs.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+use PhpCsFixer\Fixer\ArrayNotation\ArraySyntaxFixer;
+use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+use Symplify\EasyCodingStandard\ValueObject\Option;
+use Symplify\EasyCodingStandard\ValueObject\Set\SetList;
+
+return static function (ContainerConfigurator $containerConfigurator): void {
+    $services = $containerConfigurator->services();
+    $services->set(ArraySyntaxFixer::class)
+        ->call('configure', [[
+            'syntax' => 'short',
+        ]]);
+
+    $parameters = $containerConfigurator->parameters();
+    $parameters->set(Option::PATHS, [
+        __DIR__ . '/fixtures',
+        __DIR__ . '/src',
+        __DIR__ . '/tests',
+    ]);
+
+    $parameters->set
+    (Option::SETS,
+        [
+            SetList::CLEAN_CODE,
+            SetList::COMMON,
+            SetList::PSR_12,
+        ]
+    );
+
+    $parameters->set(Option::INDENTATION, "spaces");
+
+    $parameters->set(Option::LINE_ENDING, "\n");
+};