Use Doctum instead of Sami (#761)

* Use Doctum instead of Sami

- Fix .gitignore
- Move the process to docs
- Add .gitattributes

* Fix the symfony/process versions after sami was removed

Used the maximum version of 2.x and forced 3.3 before deprecation in 3.4

docs/doctum.php

@@ -0,0 +1,15 @@
+<?php
+
+use Doctum\Doctum;
+use Symfony\Component\Finder\Finder;
+
+$iterator = Finder::create()
+    ->files()
+    ->name('*.php')
+    ->in(__DIR__.'/../src/');
+
+return new Doctum($iterator, [
+    'title'                => 'PHP-FFMpeg API',
+    'build_dir'            => __DIR__.'/source/API/API',
+    'cache_dir'            => __DIR__.'/source/API/API/cache',
+]);