feat(timeline): add timeline layout

* feat(timeline): add timeline page to sidebar
* fix(timeline): fix the excerpt bugs
> Prettify the code & if <!--more--> is used when writing hexo post, show more excerpt.
* fix(timeline): fix tag & category style
> Correct spelling and float style errors.
* Add '...' after excerpts.

_config.template.yml

@@ -133,6 +133,10 @@ sidebar:
             #link: "/about"
             #icon: person
             #divider: false
+        timeline: #can use different languages
+            link: "/timeline" #create a folder named 'timeline'(due to you) within the 'source' folder
+            icon: timeline #then create a file named 'index.md' inside this folder and set 'layout' to 'timeline' in front-matter
+            divider: false
     article_num:
         use: false
         divider: false