Adding commons-math to KNOWN-IMPLEMENTATIONS

I needed to use some of the more esoteric decompositions available in Apache Commons Math.  I really liked the interface provided by core.matrix and I wanted to learn more about Clojure's protocols, so I went ahead and tried adding support.

Following your instructions in the Implementation Guide, I've added it to the KNOWN-IMPLEMENTATIONS map.

I'd appreciate any feedback you have on my implementation.  Thanks!