add snippet for sub/super diagonal

fix a few doc issues

Eigen/src/Core/Cwise.h

@@ -64,7 +64,7 @@
   * It is the return type of MatrixBase::cwise()
   * and most of the time this is the only way it is used.
   *
-  * Note that some methods are defined in the \ref Array module.
+  * Note that some methods are defined in the \ref Array_Module array module.
   *
   * Example: \include MatrixBase_cwise_const.cpp
   * Output: \verbinclude MatrixBase_cwise_const.out

Eigen/src/Core/DiagonalCoeffs.h

@@ -49,12 +49,12 @@ struct ei_traits<DiagonalCoeffs<MatrixType,DiagId> >
   enum {
     AbsDiagId = DiagId<0 ? -DiagId : DiagId,
     RowsAtCompileTime = int(MatrixType::SizeAtCompileTime) == Dynamic ? Dynamic
-                      : EIGEN_ENUM_MIN(MatrixType::RowsAtCompileTime,
-                                       MatrixType::ColsAtCompileTime) - AbsDiagId,
+                      : (EIGEN_ENUM_MIN(MatrixType::RowsAtCompileTime,
+                                        MatrixType::ColsAtCompileTime) - AbsDiagId),
     ColsAtCompileTime = 1,
     MaxRowsAtCompileTime = int(MatrixType::MaxSizeAtCompileTime) == Dynamic ? Dynamic
-                            : EIGEN_ENUM_MIN(MatrixType::MaxRowsAtCompileTime,
-                                             MatrixType::MaxColsAtCompileTime),
+                         : (EIGEN_ENUM_MIN(MatrixType::MaxRowsAtCompileTime,
+                                          MatrixType::MaxColsAtCompileTime) - AbsDiagId),
     MaxColsAtCompileTime = 1,
     Flags = (unsigned int)_MatrixTypeNested::Flags & (HereditaryBits | LinearAccessBit),
     CoeffReadCost = _MatrixTypeNested::CoeffReadCost
@@ -135,6 +135,9 @@ MatrixBase<Derived>::diagonal() const
   * The template parameter \a Id represent a super diagonal if \a Id > 0
   * and a sub diagonal otherwise. \a Id == 0 is equivalent to the main diagonal.
   *
+  * Example: \include MatrixBase_diagonal_int.cpp
+  * Output: \verbinclude MatrixBase_diagonal_int.out
+  *
   * \sa MatrixBase::diagonal(), class DiagonalCoeffs */
 template<typename Derived>
 template<int Id>

Eigen/src/Core/MatrixBase.h

@@ -34,7 +34,7 @@
   * types. Most of the Eigen API is contained in this class. Other important classes for
   * the Eigen API are Matrix, Cwise, and PartialRedux.
   *
-  * Note that some methods are defined in the \ref Array module.
+  * Note that some methods are defined in the \ref Array_Module array module.
   *
   * \param Derived is the derived type, e.g. a matrix type, or an expression, etc.
   *