whitespace correction/cleanup
add a 'copytest' to callback-test to check # of moves/copies
Change callback to use `Args...` instead of `Args&&...` which is
actually an rvalue and a 'universal reference' as its not in a deduced
context (if my understanding is correct).

This also fixes an issue where a callback's arg is a ref to a class
e.g. callback< void(foo&) >