add qr

Hey, do I revert the changes in pom.xml?

After I added this protocol, I did this in core.matrix:
```clojure
=> (def m (matrix [[1 2 3][4 5 6][7 8 9]]))
=> (set-current-implementation :vectorz)
=> (def qrr (qr m))
=> (mmul (qrr :Q) (qrr :R))
[[0.9999999999999989 1.9999999999999978 2.9999999999999973] [3.9999999999999996 5.0 5.999999999999998] [7.0 7.999999999999999 8.999999999999998]]
=> (def qrr (qr m {:return [:R]}))
=> (def r (qrr :R))
=> (def qrr (qr m {:return [:Q]}))
=> (def q (qrr :Q))
=> (mmul q r)
[[0.9999999999999989 1.9999999999999978 2.9999999999999973] [3.9999999999999996 5.0 5.999999999999998] [7.0 7.999999999999999 8.999999999999998]]
```
and it gave the expected result, but I dont know how to tell if it actually used the vectorz.