Finished integrating CaseyCarter's changes into span

tests/span_tests.cpp

@@ -1144,7 +1144,7 @@ TEST(span_test, from_array_constructor)
 
      // you can convert statically
      {
-         const span<int, 2> s2(&arr[0], 2);
+         const span<int, 2> s2{&arr[0], 2};
          static_cast<void>(s2);
      }
      {
@@ -1180,7 +1180,7 @@ TEST(span_test, from_array_constructor)
  #endif
      {
          auto f = [&]() {
-             const span<int, 4> _s4(arr2, 2);
+             span<int, 4> _s4{arr2, 2};
              static_cast<void>(_s4);
          };
          EXPECT_DEATH(f(), deathstring);