Updates to the Sparse unsupported solvers module.

* change Sparse* specialization's signatures from <..., int Backend> to <..., typename Backend>. Update SparseExtra accordingly to use structs instead of the SparseBackend enum.
* add SparseLDLT Cholmod specialization
* for Cholmod and UmfPack, SparseLU, SparseLLT and SparseLDLT now use ei_solve_retval and have the new solve() method (to be closer to the 3.0 API).

* fix doc

doc/examples/Tutorial_ReductionsVisitorsBroadcasting_broadcast_1nn.cpp~

@@ -1,24 +0,0 @@
-#include <iostream>
-#include <Eigen/Dense>
-
-using namespace std;
-using namespace Eigen;
-
-int main()
-{
-  Eigen::MatrixXf m(2,4);
-  Eigen::VectorXf v(2);
-  
-  m << 1, 2, 6, 9,
-       3, 1, 7, 2;
-       
-  v << 2,
-       3;
-
-  MatrixXf::Index index;
-  // find nearest neighbour
-  (m.colwise() - v).colwise().squaredNorm().minCoeff(&index);
-
-  cout << "Nearest neighbour is column " << index << ":" << endl;
-  cout << m.col(index) << endl;
-}

doc/examples/Tutorial_ReductionsVisitorsBroadcasting_broadcast_simple.cpp~

@@ -1,21 +0,0 @@
-#include <iostream>
-#include <Eigen/Dense>
-
-using namespace std;
-int main()
-{
-  Eigen::MatrixXf mat(2,4);
-  Eigen::MatrixXf v(2);
-  
-  mat << 1, 2, 6, 9,
-         3, 1, 7, 2;
-         
-  v << 0,
-       1;
-       
-  //add v to each column of m
-  mat.colwise() += v;
-  
-  std::cout << "Broadcasting result: " << std::endl;
-  std::cout << mat << std::endl;
-}

doc/examples/Tutorial_ReductionsVisitorsBroadcasting_reductions_norm.cpp~

@@ -1,28 +0,0 @@
-#include <Eigen/Dense>
-#include <iostream>
-
-using namespace std;
-using namespace Eigen;
-
-int main()
-{
-  VectorXf v(2);
-  MatrixXf m(2,2), n(2,2);
-  
-  v << 2,
-       5;
-  
-  m << 0,2,
-       3,4;
-
-  n << 1,2,
-       3,4;
-  
-  cout << "v.norm() = " << m.norm() << endl;
-  cout << "m.norm() = " << m.norm() << endl;
-  cout << "n.norm() = " << m.norm() << endl;
-  cout << endl;
-  cout << "v.squaredNorm() = " << v.squaredNorm() << endl;
-  cout << "m.squaredNorm() = " << m.squaredNorm() << endl;
-  cout << "n.squaredNorm() = " << n.squaredNorm() << endl;
-}

doc/examples/Tutorial_ReductionsVisitorsBroadcasting_visitors.cpp~

@@ -1,26 +0,0 @@
-#include <iostream>
-#include <Eigen/Dense>
-
-using namespace std;
-using namespace Eigen;
-
-int main()
-{
-  Eigen::MatrixXf m(2,2);
-  
-  m << 1, 2,
-       3, 4;
-
-  //get location of maximum
-  MatrixXf::Index maxRow, maxCol;
-  m.maxCoeff(&maxRow, &maxCol);
-
-  //get location of minimum
-  MatrixXf::Index minRow, minCol;
-  m.minCoeff(&minRow, &minCol);
-
-  cout << "Max at: " <<
-     maxRow << "," << maxCol << endl;
-  cout << "Min at: " <<
-     minRow << "," << minCol << endl;
-}