Small Improvements

Some little improvements to site structure

*        make disqus an include.
*        add more inf to _config.yml and change to kramdown (recommended).
*        add more itens in .gitignore
*        make script run asynchronous (references: [http://browserdiet.com/en/#async](http://browserdiet.com/en/#async), [http://www.w3schools.com/tags/att_script_async.asp](http://www.w3schools.com/tags/att_script_async.asp))
*        add readme.md (issue #3)