git-svn(1): improve asciidoc markup

git-svn(1): improve asciidoc markup

Use list continuation to have better wrapping. This accounts for most of
the changes because it reindents a lot of text without applying other
changes.

Use cross-referencing for interlinking and the gitlink macro for pointing
to other tools in the git suite.

Signed-off-by: Jonas Fonseca <fonseca@diku.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>