Better font rendering in code editor

Using `-webkit-font-smoothing: subpixel-antialiased;`, the fonts in the code editor are noticeably better rendered, thus improving readability and is also prettier.

I've attached below two screenshots (dark & light), left is without this modif, right is with :

![screen shot 2014-01-21 at 1 50 09 am](https://f.cloud.github.com/assets/949223/1959891/c8004f3c-823a-11e3-86b0-2cb5a1eec7bf.png)

![screen shot 2014-01-21 at 2 05 15 am](https://f.cloud.github.com/assets/949223/1959890/c786f7d6-823a-11e3-852b-26c0cc38c7ec.png)