Use an aligned IOFormat in the docs

doc/snippets/compile_snippet.cpp.in

@@ -4,13 +4,11 @@
 #include <Eigen/Cholesky>
 #include <Eigen/Geometry>
 
-USING_PART_OF_NAMESPACE_EIGEN
 using namespace Eigen;
 using namespace std;
 
 int main(int, char**)
 {
-  cout.precision(3);
   ${snippet_source_code}
   return 0;
 }