Added or cleaned up documentation for most of DenseMat.scala
Added or cleaned up documentation for most of DenseMat.scala

codeaudit/BIDMat,phlip9/BIDMat,codeaudit/BIDMat,phlip9/BIDMat,phlip9/BIDMat,codeaudit/BIDMat,phlip9/BIDMat,codeaudit/BIDMat,codeaudit/BIDMat,phlip9/BIDMat