Improved the layout

1. In the section "*Blog Posts*" in "*Blogging Basics*" in the official
documention of Octopress, I learnt a way to include the "Read on →"
button in the index page.
2. Removed the line numbers in atom feed with the guidances from
http://www.ewal.net/2012/09/08/octopress-customizations/#remove-line-numbers-in-atom-feed.
3. Replaced the URLs in *Extend Laptop Lifespan* with hyperlinks so as
to improve readability.