Min Bounding Circle (issue #137)

I came across this:
https://github.com/ingenuitas/SimpleCV/issues/137
when I was browsing SimpleCV issues.

I have attempted a method to implement the Min Bounding Circle functionality for Blobs
The new method has been added to SimpleCV/Features/Features.py
Method name: boundingCircle()

The code returns the (x,y,r) tuple where (x,y) is the center of the min bounding circle and r is its radius.

Kindly consider this pull request.
This is my first attempt to contribute to SimpleCV (or any open source project), so if there are any errors or if anything is lacking, please inform me so I can improve/add it.