add styling for pitches


I've been playing around with osm-bright.tm2 so thought to add some pitches to it as well. 

I followed the practice of making it as a transparent overlay as done with the forest cover. 
![z14](https://cloud.githubusercontent.com/assets/955351/2609817/c22c7ae8-bb7b-11e3-9fdc-18910d828588.png)
![z16](https://cloud.githubusercontent.com/assets/955351/2609818/c233732a-bb7b-11e3-828e-98ce0dd19f43.png)



here's some examples: