Spire integration

Hey, first off, great library. I'm one of the authors of Spire (w/ Erik Osheim @non). Looking over some of the type classes, we seem to be duplicating some work (wrt algebra type classes). Breeze has a much larger scope than Spire, so I was wondering if there was anything you'd like to see in Spire that'd let you replace breeze.math with Spire's type classes (checkout spire.algebra). A VectorSpace typeclass seems a minimum, but is there anything else?

If you all are amenable, I could try submitting a PR for a version of breeze that uses Spire's type classes where appropriate. If you aren't interested, than no worries, just le me know and I won't do the work :)

https://github.com/non/spire