feat: 增加首頁評論數顯示

fix: 修復點擊toc後，滾動完toc的highlight在點擊的上一個元素
fix: 修復打賞按鈕Hover的bug close #473
improvement: 友情鏈接界面增加title顯示（top_img設為false時）
improvement: 優化toc顯示，當向上滾動時，導航欄不會遮擋 toc close #472
improvement: 升級facebook comment sdk版本

layout/includes/header/index.pug

@@ -20,13 +20,13 @@ if !theme.disable_top_img && page.top_img !== false
     - var imgSource = top_img && top_img.indexOf('/') !== -1 ? `background-image: url('${url_for(top_img)}')` : `background: ${top_img}`
     - var bg_img = top_img ? imgSource : ''
     - var site_title = is_archive() ? _p('page.archives') : page.title || page.tag || page.category || config.title
-    - var isHomeClass = is_home() ? 'full_page' : 'not-index-bg'
+    - var isHomeClass = is_home() ? 'full_page' : 'not-home-page'
     - is_post() ? isHomeClass = 'post-bg' : isHomeClass
   else
-    - var isHomeClass = 'no-top-img'
+    - var isHomeClass = 'not-top-img'
 else
   - var top_img = false
-  - var isHomeClass = 'no-top-img'
+  - var isHomeClass = 'not-top-img'
 
 header#page-header(class=isHomeClass style=bg_img)
   !=partial('includes/header/nav', {}, {cache: true})