added some documentation to Semiring.
added some documentation to Semiring.

fixed a compile error related to move.

tjhunter/scalanlp-core,chen0031/breeze,scalanlp/breeze,ContentSquare/breeze,tjhunter/scalanlp-core,nikdon/breeze,ktakagaki/breeze,crealytics/breeze,ktakagaki/breeze,eponvert/breeze,cilier/breeze,claydonkey/breeze,sheide/breeze,calippo/breeze,mredaelli/breeze,wstcpyt/breeze