bugfix,init page object's lexed attribute.

the page object's attribute 'lexed' is not correctly inited.so when
use page.lexed to generate the search index file,nothing will be
indexed.

lib/generate/site/index.js

@@ -120,7 +120,7 @@ Generator.prototype.prepareFile  = function(content, _input) {
     .then(function() {
         // Lex, parse includes and get
         // Get HTML generated sections
-        return parse.page(page.content, {
+        return parse.page(page, {
             // Local files path
             dir: path.dirname(_input) || '/',
             // Project's include folder

lib/parse/page.js

@@ -47,11 +47,12 @@ function quizQuestion(node) {
     }
 }
 
-function parsePage(src, options) {
+function parsePage(page, options) {
     options = options || {};
 
     // Lex if not already lexed
-    return (_.isArray(src) ? src : lex(include(src, [options.dir, options.includes_dir], options.variables)))
+    page.lexed = (_.isArray(page.content) ? page.content : lex(include(page.content, [options.dir, options.includes_dir], options.variables)))
+    return page.lexed
     .map(function(section) {
         // Transform given type
         if(section.type === 'exercise') {