MOTIVATION:
* When you post a link on facebook normaly with your browser, facebook automatically detects a featured image of the link (web page).
  However, if you post a link through facebook API, it doesn't.
  So, I needed to develop a similar detection tool which takes url as an argument and returns a featured image of the page.
  This library contains tiny algorithm to do that.

TODO:
* make into npm package format.
* rewrite this README.
* deploy web API and command line API.