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/phpunit.xml

@@ -1,17 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:noNamespaceSchemaLocation="./vendor/phpunit/phpunit/phpunit.xsd"
-         bootstrap="vendor/autoload.php"
-         colors="true"
->
-    <testsuites>
-        <testsuite name="AllTests">
-            <directory>./tests</directory>
-        </testsuite>
-    </testsuites>
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">./src</directory>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd" bootstrap="vendor/autoload.php" colors="true">
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">./src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="AllTests">
+      <directory>./tests</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>