Use Uri to manage paths internally.

Nothing revolutionary but it kills the enum.

```
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] Picasso (Parent) .................................. SUCCESS [0.711s]
[INFO] Picasso ........................................... SUCCESS [10.222s]
[INFO] Picasso Sample .................................... SUCCESS [7.087s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 18.998s
[INFO] Finished at: Sat May 25 03:36:16 PDT 2013
[INFO] Final Memory: 36M/217M
[INFO] ------------------------------------------------------------------------
```