Add `h5save` function.

Adds simple-to-use function to directly write a dataset into a HDF5 file in the same simply manner as saveraw can be used.

Instead of h5create and than h5write you directly can use h5save, see example below.

   % simple storing of array
   data = ones(12, 4);
   h5save("test.h5", "/data", data);
   h5info("test.h5", "/data")

   % update stored array (only possible for same data type and size)
   data = zeros(size(data));
   h5save("test.h5", "/data", data);