add gfm code blocks

lib/marked.js

@@ -12,6 +12,7 @@
 var block = {
   newline: /^\n+/,
   code: /^ {4,}[^\n]*(?:\n {4,}[^\n]*|\n)*(?=\n| *$)/,
+  gfm_code: /^ *``` *(\w+)? *\n([^\0]+?)\s*```(?= *\n| *$)/,
   hr: /^( *[\-*_]){3,} *\n/,
   heading: /^ *(#{1,6}) *([^\0]+?) *#* *\n+/,
   lheading: /^([^\n]+)\n *(=|-){3,}/,
@@ -82,6 +83,17 @@ block.token = function(str, tokens) {
       continue;
     }
 
+    // gfm_code
+    if (cap = block.gfm_code.exec(str)) {
+      str = str.substring(cap[0].length);
+      tokens.push({
+        type: 'code',
+        lang: cap[1],
+        text: cap[2]
+      });
+      continue;
+    }
+
     // heading
     if (cap = block.heading.exec(str)) {
       str = str.substring(cap[0].length);