Methods getAdditionalParams & setAdditionalParams which allow the user to pass additional parameters to the encoding request (#284)

* Modification of the format Video to add additional parameters based on user's desire
* Update of the README
* Working version of this feature. Still needs tests
* Fixing the tests of FFMPeg\Media\Video
* Setting up tests for the additionalParams feature
* Correction des tests
* Modifying tests. They work locally but not on Travis.
* Still trying to understand why Travis is throwing errors when PHPUnit is not.
* Add the additional params at the end of the command
* Fixed the tests and the way we add the parameters
* We remove log files

src/FFMpeg/Media/Video.php

@@ -120,6 +120,15 @@ class Video extends Audio
             }
         }
 
+        // If the user passed some additional parameters
+        if ($format instanceof VideoInterface) {
+            if (null !== $format->getAdditionalParameters()) {
+                foreach ($format->getAdditionalParameters() as $additionalParameter) {
+                    $commands[] = $additionalParameter;
+                }
+            }
+        }
+
         $fs = FsManager::create();
         $fsId = uniqid('ffmpeg-passes');
         $passPrefix = $fs->createTemporaryDirectory(0777, 50, $fsId) . '/' . uniqid('pass-');