Apply clang-tidy modernize-use-using to all tests (#199)

Run clang-tidy 7.0 with `-checks='-*,modernize-use-using' -fix`
against TU-s of all tests.

Manually refactor numerous typedef-s
- where missed by modernize-use-using check, not uncommon
- in code snippets in comments

Outcome is that searching for lower-case whole word typedef
in sources of all the tests should return no matches.

test/recreate_image.cpp

@@ -60,7 +60,7 @@ template< typename View
 std::size_t total_allocated_size_in_bytes( const typename View::point_t& dimensions )
 {
 
-    typedef typename View::x_iterator x_iterator;
+    using x_iterator = typename View::x_iterator;
 
     // when value_type is a non-pixel, like int or float, num_channels< ... > doesn't work.
     const std::size_t _channels_in_image = mpl::eval_if< is_pixel< typename View::value_type >