Add ability to hide non-diff lines

Sometimes it's desirable to only show lines that have changed, even if
it means stripping all context from the diff.

Author: djmattyg007

src/Differ.php

@@ -24,6 +24,11 @@ class Differ
      */
     private $header;
 
+    /**
+     * @var bool
+     */
+    private $showNonDiffLines = true;
+
     /**
      * @param string $header
      */
@@ -32,6 +37,14 @@ public function __construct($header = "--- Original\n+++ New\n")
         $this->header = $header;
     }
 
+    /**
+     * @param bool $show
+     */
+    public function setShowNonDiffLines($show)
+    {
+        $this->showNonDiffLines = $show;
+    }
+
     /**
      * Returns the diff between two arrays or strings as string.
      *
@@ -90,15 +103,17 @@ public function diff($from, $to, LongestCommonSubsequence $lcs = null)
             }
 
             if ($newChunk) {
-                $buffer  .= "@@ @@\n";
+                if ($this->showNonDiffLines === true) {
+                    $buffer  .= "@@ @@\n";
+                }
                 $newChunk = false;
             }
 
             if ($diff[$i][1] === 1 /* ADDED */) {
                 $buffer .= '+' . $diff[$i][0] . "\n";
             } elseif ($diff[$i][1] === 2 /* REMOVED */) {
                 $buffer .= '-' . $diff[$i][0] . "\n";
-            } else {
+            } elseif ($this->showNonDiffLines === true) {
                 $buffer .= ' ' . $diff[$i][0] . "\n";
             }
         }