Post formatting

https://en.wikipedia.org/wiki/Example.com
https://en.wikipedia.org/wiki/URL
Each post is just an ordinary Git commit, but consisting only of log
message. You can easily create that kind of commits with:

    $ git commit --allow-empty

Each post has the title: it is just its first line, separated with the
blank line from the remaining body. Well, again, just like with ordinary
commits.

If first lines of a body are URLs, then their domains will be displayed
on the index page. It is convenient to see that some post relates to
YouTube video, some kind of news website and so on.