Docs folder standardization and other fixes

docs/internals.md

@@ -0,0 +1,46 @@
+# Internals
+
+## Unit testing
+
+The package is tested with [PHPUnit](https://phpunit.de/). To run tests:
+
+```shell
+./vendor/bin/phpunit
+```
+
+## Mutation testing
+
+The package tests are checked with [Infection](https://infection.github.io/) mutation framework with
+[Infection Static Analysis Plugin](https://github.com/Roave/infection-static-analysis-plugin). To run it:
+
+```shell
+./vendor/bin/roave-infection-static-analysis-plugin
+```
+
+## Static analysis
+
+The code is statically analyzed with [Psalm](https://psalm.dev/). To run static analysis:
+
+```shell
+./vendor/bin/psalm
+```
+
+## Rector
+
+Use [Rector](https://github.com/rectorphp/rector) to make codebase follow some specific rules or
+use either newest or any specific version of PHP:
+
+```shell
+./vendor/bin/rector
+```
+
+## Dependencies
+
+Use [ComposerRequireChecker](https://github.com/maglnet/ComposerRequireChecker) to detect transitive
+[Composer](https://getcomposer.org/) dependencies.
+
+To run the checker, execute the following command:
+
+```shell
+./vendor/bin/composer-require-checker
+```

psalm.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0"?>
 <psalm
     errorLevel="1"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
     xmlns="https://getpsalm.org/schema/config"
     xsi:schemaLocation="https://getpsalm.org/schema/config vendor/vimeo/psalm/config.xsd"
 >

src/Json.php

@@ -33,7 +33,7 @@ final class Json
      *
      * @param mixed $value The data to be encoded.
      * @param int $options The encoding options. For more details please refer to
-     * {@see http://www.php.net/manual/en/function.json-encode.php}.
+     * {@see https://www.php.net/manual/en/function.json-encode.php}.
      * Default is `JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR`.
      * @param int $depth The maximum depth.
      *