plumbing: format/idxfile, avoid creating temporary buffers to decode integers
plumbing: format/idxfile, avoid creating temporary buffers to decode integers

Signed-off-by: Filip Navara <9b185aee7645c223a53be9a22ba0c35ad732e79f@gmail.com>

go-git/go-git,mcuadros/go-git,go-git/go-git,src-d/go-git,mcuadros/go-git,src-d/go-git