Feature/change string replace

![results_new](https://f.cloud.github.com/assets/2396815/572374/415c245e-c798-11e2-92e9-2fa840c77499.png)
![results_old](https://f.cloud.github.com/assets/2396815/572375/415fe206-c798-11e2-940f-93e91345a461.png)

Just to make sure, I've tested out the times between the two methods in my PC and  `string.Template` turned out to be ((232-187)/232 =) 19% faster than `__str__.replace`