Allow arbitrary metadata separator

Separator is any character sequence from start of file to first newline.

For example:
    ```
    title = "Whatever"
    ```
    # Hello
is now possible

sitegin/parseHugo.js

@@ -5,16 +5,15 @@ var jsesc = require('jsesc')
 
 var readPageWorker = function(content, obj) {
   if(content === undefined) throw new Error('content is undefined');
-  var head = content.substring(0,4)
-  if(head !== '+++\n')
-    throw new Error('Failed to parse file '+obj.filename+':\n'+
-                    'Wrong header (expected "+++\\n" got "'+jsesc(head)+'")')
-
-  content = content.substring(4);
-  var fmEnd = content.indexOf('+++\n');
+  var headLength = content.indexOf('\n')+1;
+  var head = content.substring(0,headLength)
+  content = content.substring(headLength);
+  var fmEnd = content.indexOf(head);
   if(fmEnd < 0) {
     console.log(jsesc(content));
-    throw new Error('Cannot find terminating +++\n in file '+obj.filename);
+    throw new Error('Cannot find terminating '+
+      head.substring(0,headLength-1)+
+      '\n in file '+obj.filename);
   }
   obj.content = content.substring(fmEnd+4);
   try {