Add readFile method to Filesystem component

Filesystem.php

@@ -478,4 +478,22 @@ private function toIterator($files)
 
         return $files;
     }
+
+    /**
+     * Read file and return contents.
+     *
+     * @param $filename
+     *
+     * @return string $filename The file to read.
+     *
+     * @throws Exception\IOException
+     */
+    public function readFile($filename)
+    {
+        if (false === $source = @file_get_contents($filename)) {
+            throw new IOException(sprintf('Failed to read "%s" because source file could not be opened for reading.', $filename), 0, null, $filename);
+        }
+
+        return $source;
+    }
 }

README.md

@@ -33,6 +33,9 @@ $filesystem->makePathRelative($endPath, $startPath);
 $filesystem->mirror($originDir, $targetDir, \Traversable $iterator = null, $options = array());
 
 $filesystem->isAbsolutePath($file);
+
+$filesystem->readFile($file);
+
 ```
 
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