Adds minification durations to the results

Preview:
![capture d ecran 2014-11-06 a 16 09 13](https://cloud.githubusercontent.com/assets/477089/4937848/150160e4-65c7-11e4-9f11-c4afd60b11e6.png)
![capture d ecran 2014-11-06 a 16 10 23](https://cloud.githubusercontent.com/assets/477089/4937849/18afdf86-65c7-11e4-8437-a1479a30ad12.png)

Close #21