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/tests/ApprovalTest.php

@@ -1,24 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Tests;
-
-use ApprovalTests\Approvals;
-use PHPUnit\Framework\TestCase;
-
-class ApprovalTest extends TestCase
-{
-    public function testTestFixture(): void
-    {
-        $argv[0] = 'texttest_fixture.php';
-        $argv[1] = 31;
-
-        ob_start();
-        require_once __DIR__ . '/../fixtures/texttest_fixture.php';
-        $output = ob_get_contents();
-        ob_end_clean();
-
-        Approvals::verifyString($output);
-    }
-}