Add Disqus support

[sudix]

Since I want to use Disqus in my blog with nofancy, I made this PR.

I borrowed some ides from enten/hyde-y.

Config

Add disqusShortname value to config file like below.

config.toml

baseurl = "http://blog.example.com/"
title = "some blog"
theme = "nofancy"
disqusShortname = "disqusshortname" # <- HERE!

[permalinks]
    post = "/posts/:year/:month/:slug/"