Bugfixes and improvements

* Implemented the --image option
* Implemented the --write-state option to go with --check
* Fixed bug in Lockfile class

src/State/Lockfile.php

@@ -17,7 +17,7 @@ class Lockfile
     public function lock()
     {
         if (file_exists($this->filename)) {
-            if (time() - filemtime($this->filename) < $this-$maxLock) {
+            if (time() - filemtime($this->filename) < $this->maxLock) {
                 throw new \RuntimeException("Lockfile {$this->filename} already exists");
             }
         }