doc and use sed to clean the class hierarchy instead of

preprocessor directives.

Eigen/src/Core/DiagonalCoeffs.h

@@ -60,11 +60,7 @@ struct ei_traits<DiagonalCoeffs<MatrixType> >
 };
 
 template<typename MatrixType> class DiagonalCoeffs
-#ifndef EIGEN_PARSED_BY_DOXYGEN
    : public MatrixBase<DiagonalCoeffs<MatrixType> >
-#else
-  : public MatrixBase
-#endif
 {
   public: