SLIC Superpixels implemented

### SUMMARY

 - SLIC based Superpixel segmentation implemented. (Issue #8)
 - Image.copy() bug resolved (Issue #34)
 - Blob.meanColor() bug resolved (Issue #35)


### Superpixels

``` python

img = Image("lenna")
sp = img.segmentSuperpixels(400, 40)
sp.show()
sp.clusterWithColorMeans().show()
```

![lenna40040](https://f.cloud.github.com/assets/1256649/1094406/57208dcc-16c9-11e3-806f-96ea5611f918.jpg)

![lennacluster40040](https://f.cloud.github.com/assets/1256649/1094408/67a6d6ce-16c9-11e3-9af9-8055af0b6bbd.jpg)