feat: restructure docs into "chapters" (#12)

* feat(docker, k8s): create containers folder and kubernetes notes

docs/languages/php/composer.md

@@ -0,0 +1,109 @@
+# Composer & Autoloading
+
+## Autoloading
+
+The function [spl_autoload_register()](https://www.php.net/manual/en/function.spl-autoload-register.php) allows to register a function that will be invoked when PHP needs to load a class/interface defined by the user.
+
+In `autoload.php`:
+
+```php
+# custom function
+function autoloader($class) {
+
+
+    # __DIR__ -> path of calling file
+    # $class -> className (hopefully same as file)
+    # if class is in namespace $class -> Namespace\className (hopefully folders mirror Namespace)
+
+    $class = str_replace("\\", DIRECTORY_SEPARATOR, $class);  # avoid linux path separator issues
+
+    $fileName = sprintf("%s\\path\\%s.php", __DIR__, $class);  
+    # or
+    $filename = sprintf("%s\\%s.php", __DIR__, $class);  # if class is in namespace
+
+    if (file_exists($fileName)) {
+        include $fileName;
+    }
+}
+
+spl_autoload_register('autoloader');  // register function
+```
+
+In `file.php`:
+
+```php
+require "autoload.php";
+
+# other code
+```
+
+> **Note**: will fuck up if namespaces exists.
+
+### Multiple Autoloading
+
+It's possible to resister multiple autoloading functions by calling `spl_autoload_register()` multiple times.
+
+```php
+# prepend adds the function at the start of the queue
+# throws selects if errors in loading throw exceptions
+spl_autoload_register(callable $func, $throw=TRUE, $prepend=FALSE);
+
+spl_autoload_functions()  # return a list of registered functions.
+```
+
+## [Composer](https://getcomposer.org/)
+
+Open Source project for dependency management and autoloading of PHP libraries and classes.
+
+Composer uses `composer.json` to define dependencies with third-party libraries.
+Libraries are downloaded through [Packagist](https://packagist.org/) and [GitHub](https://github.com/).
+
+In `composer.json`:
+
+```json
+{
+    "require": {
+        "php": ">=7.0",
+        "monolog/monolog": "1.0.*"
+    }
+}
+```
+
+### Installing Dependencies
+
+In the same folder of `composer.json` execute `composer install`.
+
+Composer will create:
+
+- `vendor`: folder containing all requested libraries
+- `vendor\autoload.php`: file for class autoloading
+- `composer.lock`
+
+In alternative `composer require <lib>` will add the library to the project and create a `composer.json` if missing.
+
+> **Note**: to ignore the php version use `composer <command> --ignore-platform-reqs`
+
+### Updating Dependencies
+
+To update dependencies use `composer update`. To update only the autoloading section use `composer dump-autoload`.
+
+### [Autoloading Project Classes](https://getcomposer.org/doc/04-schema.md#autoload)
+
+[PSR-4 Spec](https://www.php-fig.org/psr/psr-4/)
+
+Composer can also autoload classes belonging to the current project. It's sufficient to add the `autoload` keyword in the JSON and specify the path and autoload mode.
+
+```json
+{
+    "autoload": {
+        "psr-4": {
+            "RootNamespace": "src/",
+            "Namespace\\": "src/Namespace/",
+            },
+        "file": [
+            "path/to/file.php",
+            ...
+        ]
+    }
+}
+```