[RFC 0/4] ref-filter: remove printing from formatting logic

["Оля Тележная" <olyatelezhnaya@gmail.com>]

The main idea of the patch is, if you want to format the output by
ref-filter, you should have an ability to work with errors by yourself
if you want to.
So I decided not to touch signature of show_ref_array_item(), but to
move all printing (I mean errors) to it. So that we could invoke
format_ref_array_item() and be sure that we cold handle errors by
ourselves.

The patch is not finished, but I decided to show it to you. There are
still many places where we could die in the middle of formatting
process. But, if you like the general idea, I will finish and re-send
it.

Another question is about verify_ref_format(). Do we need to allow its
users also to manage errors by themselves? I left the old scenario,
printing everything in verify_ref_format() and die. If you have better
ideas, please share them.

Thanks a lot!
Olga