Site Improvements

Some changes i have added into the project:

-  Reduced excessive margins in h2, h3 ( 520392f988fb88b85add4a6c07df5f21df4ec286 )
-  Make twitter script run asynchronously ( 24e616df1626f64d688675ed470b9930a36bda97 )
   - References: [Google Developers](https://developers.google.com/speed/docs/insights/UseAsync), [w3schools](http://www.w3schools.com/tags/att_script_async.asp)
-  Added social media tags, used by open graph protocol ( d8393acd162b208ccbb0c6f1028ecdb3923c3ca8 )
   -  Reference: [OGP](http://ogp.me/)
-  Added viewport tag and use media queries to apply flexibility to site ( d8393acd162b208ccbb0c6f1028ecdb3923c3ca8 , ab57a8f9d4a9405013c2352c89576c01918faca2 , d60c23d3245ac85135c6bbbb530cb13f7eea66be )

**Some screenshots about the last change:**

Samsung Galaxy Note ||:
![captura de tela 2014-07-23 as 23 29 42](https://cloud.githubusercontent.com/assets/3630346/3683022/71454072-12da-11e4-9a42-89e6906f29bb.png)

HTC one X:
![captura de tela 2014-07-23 as 23 31 34](https://cloud.githubusercontent.com/assets/3630346/3683042/aed5f0d0-12da-11e4-8309-d7eee35e0051.png)

Samsung Galaxy S4:
![captura de tela 2014-07-23 as 22 13 20](https://cloud.githubusercontent.com/assets/3630346/3682782/9d39bb36-12d5-11e4-90fc-06bfef269e41.png)

Google Nexus 4:
![captura de tela 2014-07-23 as 22 13 57](https://cloud.githubusercontent.com/assets/3630346/3682784/9fd240fc-12d5-11e4-9dea-279db92b0521.png)

@sindresorhus changed in 2ceac892aa7dc08ddfc49fff2e6b4173c5c096f9 :octocat: