add support for vectorization library VC

This branch adds support for the Vc library, which add support for vectorization, including an abstraction for intrisics.

We have been using in EXA-Dune and I belive that the integration of vectorization support into the core-Dune is something Dune in general can benefit from. A separate branch I'm preparing for ISTL will add support for multiple RHS vectors using vectorization.

The branch collects a set of helper classes which allow to add vectorization support to your code with moderate effort. Mainly this means that we have a couple of utility functions, which work for scalar data types, ranges and SIMD data types alike.

dune/common/typetraits.hh

@@ -531,6 +531,25 @@ namespace Dune
 
 #endif // defined(DOXYGEN) or HAVE_IS_INDEXABLE_SUPPORT
 
+  /**
+     typetrait to check that a class has begin() and end() members
+   */
+  // default version, gets picked if SFINAE fails
+  template<typename T, typename = void, typename = void>
+  struct is_range
+    : public std::false_type
+  {};
+
+#ifndef DOXYGEN
+  // version for types with begin() and end()
+  template<typename T>
+  struct is_range<T,
+                  decltype(Std::declval<T>().begin()),
+                  decltype(Std::declval<T>().end())>
+    : public std::true_type
+  {};
+#endif
+
   namespace detail
   {
     ///