Add k-means example using NormedVectorSpaces.
Add k-means example using NormedVectorSpaces.

An illustrative example of why abstracting over vector spaces can make
our code more re-usable.

adampingel/spire,non/spire,codeaudit/spire,AlecZorab/spire,tixxit/spire,AlecZorab/spire,guersam/spire,guersam/spire,kevinmeredith/spire,woparry/spire,JackSullivan/spire,rklaehn/spire,siddhartha-gadgil/spire,codeaudit/spire,adampingel/spire,kevinmeredith/spire,non/spire,woparry/spire,siddhartha-gadgil/spire,JackSullivan/spire,rklaehn/spire,tixxit/spire