Improve inline code sample styles

Old:

![code samples old](https://f.cloud.github.com/assets/808159/845676/68115fd8-f3ee-11e2-832f-9829623967ac.png)

New:

![code samples new](https://f.cloud.github.com/assets/808159/845677/6acd7f54-f3ee-11e2-9dc0-2630af3e691c.png)

Lighter, easier to read, less obtrusive.