Allow PHP 8.0 and upgraded PHPUnit to version 9

The PHPUnit XML configuration was migrated also.

 - phpunit/phpunit-mock-objects removed (installed version was 5.0.10)

 - phpunit/php-token-stream removed (installed version was 2.0.2)

 - symfony/polyfill-ctype updated from v1.19.0 to v1.22.1
   See changes: symfony/polyfill-ctype@v1.19.0...v1.22.1
   Release notes: https://github.com/symfony/polyfill-ctype/releases/tag/v1.22.1

 - webmozart/assert updated from 1.9.1 to 1.10.0
   See changes: webmozarts/assert@1.9.1...1.10.0
   Release notes: https://github.com/webmozarts/assert/releases/tag/1.10.0

 - phpdocumentor/reflection-common updated from 1.0.1 to 2.2.0
   See changes: phpDocumentor/ReflectionCommon@1.0.1...2.2.0
   Release notes: https://github.com/phpDocumentor/ReflectionCommon/releases/tag/2.2.0

 - phpdocumentor/type-resolver updated from 0.5.1 to 1.4.0
   See changes: phpDocumentor/TypeResolver@0.5.1...1.4.0
   Release notes: https://github.com/phpDocumentor/TypeResolver/releases/tag/1.4.0

 - phpdocumentor/reflection-docblock updated from 4.3.4 to 5.2.2
   See changes: phpDocumentor/ReflectionDocBlock@4.3.4...5.2.2
   Release notes: https://github.com/phpDocumentor/ReflectionDocBlock/releases/tag/5.2.2

 - sebastian/version updated from 2.0.1 to 3.0.2
   See changes: sebastianbergmann/version@2.0.1...3.0.2
   Release notes: https://github.com/sebastianbergmann/version/releases/tag/3.0.2

 - sebastian/type installed in version 2.3.1
   Release notes: https://github.com/sebastianbergmann/type/releases/tag/2.3.1

 - sebastian/resource-operations updated from 1.0.0 to 3.0.3
   See changes: sebastianbergmann/resource-operations@1.0.0...3.0.3
   Release notes: https://github.com/sebastianbergmann/resource-operations/releases/tag/3.0.3

 - sebastian/recursion-context updated from 3.0.1 to 4.0.4
   See changes: sebastianbergmann/recursion-context@3.0.1...4.0.4
   Release notes: https://github.com/sebastianbergmann/recursion-context/releases/tag/4.0.4

 - sebastian/object-reflector updated from 1.1.2 to 2.0.4
   See changes: sebastianbergmann/object-reflector@1.1.2...2.0.4
   Release notes: https://github.com/sebastianbergmann/object-reflector/releases/tag/2.0.4

 - sebastian/object-enumerator updated from 3.0.4 to 4.0.4
   See changes: sebastianbergmann/object-enumerator@3.0.4...4.0.4
   Release notes: https://github.com/sebastianbergmann/object-enumerator/releases/tag/4.0.4

 - sebastian/global-state updated from 2.0.0 to 5.0.2
   See changes: sebastianbergmann/global-state@2.0.0...5.0.2
   Release notes: https://github.com/sebastianbergmann/global-state/releases/tag/5.0.2

 - sebastian/exporter updated from 3.1.3 to 4.0.3
   See changes: sebastianbergmann/exporter@3.1.3...4.0.3
   Release notes: https://github.com/sebastianbergmann/exporter/releases/tag/4.0.3

 - sebastian/environment updated from 3.1.0 to 5.1.3
   See changes: sebastianbergmann/environment@3.1.0...5.1.3
   Release notes: https://github.com/sebastianbergmann/environment/releases/tag/5.1.3

 - sebastian/diff updated from 2.0.1 to 4.0.4
   See changes: sebastianbergmann/diff@2.0.1...4.0.4
   Release notes: https://github.com/sebastianbergmann/diff/releases/tag/4.0.4

 - sebastian/comparator updated from 2.1.3 to 4.0.6
   See changes: sebastianbergmann/comparator@2.1.3...4.0.6
   Release notes: https://github.com/sebastianbergmann/comparator/releases/tag/4.0.6

 - sebastian/code-unit installed in version 1.0.8
   Release notes: https://github.com/sebastianbergmann/code-unit/releases/tag/1.0.8

 - sebastian/cli-parser installed in version 1.0.1
   Release notes: https://github.com/sebastianbergmann/cli-parser/releases/tag/1.0.1

 - phpunit/php-timer updated from 1.0.9 to 5.0.3
   See changes: sebastianbergmann/php-timer@1.0.9...5.0.3
   Release notes: https://github.com/sebastianbergmann/php-timer/releases/tag/5.0.3

 - phpunit/php-text-template updated from 1.2.1 to 2.0.4
   See changes: sebastianbergmann/php-text-template@1.2.1...2.0.4
   Release notes: https://github.com/sebastianbergmann/php-text-template/releases/tag/2.0.4

 - phpunit/php-invoker installed in version 3.1.1
   Release notes: https://github.com/sebastianbergmann/php-invoker/releases/tag/3.1.1

 - phpunit/php-file-iterator updated from 1.4.5 to 3.0.5
   See changes: sebastianbergmann/php-file-iterator@1.4.5...3.0.5
   Release notes: https://github.com/sebastianbergmann/php-file-iterator/releases/tag/3.0.5

 - theseer/tokenizer updated from 1.1.3 to 1.2.0
   See changes: theseer/tokenizer@1.1.3...1.2.0
   Release notes: https://github.com/theseer/tokenizer/releases/tag/1.2.0

 - nikic/php-parser installed in version v4.10.5
   Release notes: https://github.com/nikic/PHP-Parser/releases/tag/v4.10.5

 - sebastian/lines-of-code installed in version 1.0.3
   Release notes: https://github.com/sebastianbergmann/lines-of-code/releases/tag/1.0.3

 - sebastian/complexity installed in version 2.0.2
   Release notes: https://github.com/sebastianbergmann/complexity/releases/tag/2.0.2

 - sebastian/code-unit-reverse-lookup updated from 1.0.2 to 2.0.3
   See changes: sebastianbergmann/code-unit-reverse-lookup@1.0.2...2.0.3
   Release notes: https://github.com/sebastianbergmann/code-unit-reverse-lookup/releases/tag/2.0.3

 - phpunit/php-code-coverage updated from 5.3.2 to 9.2.6
   See changes: sebastianbergmann/php-code-coverage@5.3.2...9.2.6
   Release notes: https://github.com/sebastianbergmann/php-code-coverage/releases/tag/9.2.6

 - doctrine/instantiator updated from 1.0.5 to 1.4.0
   See changes: doctrine/instantiator@1.0.5...1.4.0
   Release notes: https://github.com/doctrine/instantiator/releases/tag/1.4.0

 - phpspec/prophecy updated from v1.10.3 to 1.13.0
   See changes: phpspec/prophecy@v1.10.3...1.13.0
   Release notes: https://github.com/phpspec/prophecy/releases/tag/1.13.0

 - phar-io/version updated from 1.0.1 to 3.1.0
   See changes: phar-io/version@1.0.1...3.1.0
   Release notes: https://github.com/phar-io/version/releases/tag/3.1.0

 - phar-io/manifest updated from 1.0.1 to 2.0.1
   See changes: phar-io/manifest@1.0.1...2.0.1
   Release notes: https://github.com/phar-io/manifest/releases/tag/2.0.1

 - myclabs/deep-copy updated from 1.7.0 to 1.10.2
   See changes: myclabs/DeepCopy@1.7.0...1.10.2
   Release notes: https://github.com/myclabs/DeepCopy/releases/tag/1.10.2

 - phpunit/phpunit updated from 6.5.14 to 9.5.4
   See changes: sebastianbergmann/phpunit@6.5.14...9.5.4
   Release notes: https://github.com/sebastianbergmann/phpunit/releases/tag/9.5.4

Author: Kekos

composer.json

@@ -12,12 +12,12 @@
         }
     ],
     "require": {
-        "php": "^7.0",
+        "php": "^7.0 || ~8.0",
         "psr/http-message": "^1.0"
     },
     "require-dev": {
         "guzzlehttp/psr7": "^1.3",
-        "phpunit/phpunit": "^6.0",
+        "phpunit/phpunit": "^9.0",
         "squizlabs/php_codesniffer": "^3.3"
     },
     "autoload": {
@@ -33,7 +33,7 @@
     "config": {
         "sort-packages": true,
         "platform": {
-            "php": "7.0"
+            "php": "8.0"
         }
     },
     "scripts": {