Please review my code

Hi everyone, I haven't sent the code by mailing lists because 25 commits (every commit in separate message) look like a spam.

Please look at my code: https://github.com/telezhnaya/git/commits/catfile You could send me any ideas here or in Github.

The main idea of the patch is to get rid of using custom formatting in cat-file and start using general one from ref-filter. Additional bonus is that cat-file becomes to support many new formatting commands like %(if), %(color), %(committername) etc.

I remember I need to rewrite docs, I will do that in the near future.

I would be happy to get any ideas from you. Thanks! Olga