Add a coverage command

.gitignore

@@ -2,4 +2,5 @@
 /var
 /.php_cs
 /.idea
-/*.cache
\ No newline at end of file
+/*.cache
+/_coverage
\ No newline at end of file

composer.json

@@ -59,6 +59,9 @@
         ],
         "cs": [
             "@php vendor/bin/php-cs-fixer --ansi fix --dry-run --diff --diff-format=udiff"
+        ],
+        "coverage": [
+            "@php vendor/bin/simple-phpunit --coverage-html _coverage"
         ]
     }
 }
\ No newline at end of file