[PATCH] Documentation: Add asciidoc.conf file and gitlink: macro

[PATCH] Documentation: Add asciidoc.conf file and gitlink: macro

Introduce an asciidoc.conf file with the purpose of adding a gitlink:
macro which will improve the manpage output.

Original cogito patch by Jonas Fonseca <fonseca@diku.dk>;
asciidoc.conf from that patch was further enhanced to use the proper
DocBook tag <citerefentry> for references to man pages.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Junio C Hamano <junkio@cox.net>