* add Regression module, from eigen1, improved, with doc and unit-test.

* fix .normalized() so that Random().normalized() works; since the return
type became complicated to write down i just let it return an actual
vector, perhaps not optimal.
* add Sparse/CMakeLists.txt. I suppose that it was intentional that it
didn't have CMakeLists, but in <=2.0 releases I'll just manually remove
Sparse.

Eigen/src/LU/LU.h

@@ -335,7 +335,9 @@ bool LU<MatrixType>::solve(
   return true;
 }
 
-/** \return the LU decomposition of \c *this.
+/** \lu_module
+  *
+  * \return the LU decomposition of \c *this.
   *
   * \sa class LU
   */