doc: Fixed index syntax.

Signed-off-by: John Wilkins <jowilkin@redhat.com>
doc: Added rbd-replay-many and restructured index.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Reformatting on rbd replay doc.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>