Make GetObjectObject#body always be IO

[carlhoerberg]

Currently code using this has to check which type it is.

[taylorfinnell]

I have not looked at it much, but this throws errors when you run the object_put_get.cr example in examples/

[carlhoerberg]

Ok, yes, this patch isn't backward compatible. puts resp.body will raise as there's no IO#to_s. One way to still be backward compatible is to add a GetObjectOutput#body_io instead.

[carlhoerberg]

Otherwise, to fix the example you just change the last line to puts resp.body.gets_to_end, or the very more efficient IO.copy resp.body, STDOUT

[carlhoerberg]

Created a new class for streamed objects, which only got the body_io, normal synchronus get_object now only got body and it's always a string.

[taylorfinnell]

Thank you!