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/fixtures/texttest_fixture.php

@@ -1,13 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 require_once __DIR__ . '/../vendor/autoload.php';
 
 use GildedRose\GildedRose;
 use GildedRose\Item;
 
-echo "OMGHAI!" . PHP_EOL;
+echo 'OMGHAI!' . PHP_EOL;
 
-$items = array(
+$items = [
     new Item('+5 Dexterity Vest', 10, 20),
     new Item('Aged Brie', 2, 0),
     new Item('Elixir of the Mongoose', 5, 7),
@@ -17,8 +19,8 @@ $items = array(
     new Item('Backstage passes to a TAFKAL80ETC concert', 10, 49),
     new Item('Backstage passes to a TAFKAL80ETC concert', 5, 49),
     // this conjured item does not work properly yet
-    new Item('Conjured Mana Cake', 3, 6)
-);
+    new Item('Conjured Mana Cake', 3, 6),
+];
 
 $app = new GildedRose($items);
 
@@ -28,8 +30,8 @@ if (count($argv) > 1) {
 }
 
 for ($i = 0; $i < $days; $i++) {
-    echo("-------- day $i --------" . PHP_EOL);
-    echo("name, sellIn, quality" . PHP_EOL);
+    echo "-------- day ${i} --------" . PHP_EOL;
+    echo 'name, sellIn, quality' . PHP_EOL;
     foreach ($items as $item) {
         echo $item . PHP_EOL;
     }