Digamma cleanup

* Added permission from cephes author to use his code
* Cleanup in ArrayCwiseUnaryOps

Eigen/src/plugins/ArrayCwiseUnaryOps.h

@@ -320,9 +320,6 @@ lgamma() const
 }
 
 /** \returns an expression of the coefficient-wise digamma (psi, derivative of lgamma).
- *
- * Example: \include Cwise_digamma.cpp
- * Output: \verbinclude Cwise_digamma.out
  *
  * \sa cos(), sin(), tan()
  */