update non-menu authoring guides

[stanwebber]

i notice all the basic authoring guides with 1 exception indicate track-at-once mode in screenshots. i realize in the grand scheme of things this setting makes next to no difference, but if you have to recommend one or the other i'd say disc-at-once is more appropriate. the only reason i bring this up at all is i'd like to link to these guides. i imagine it wouldn't hurt to bring guides up to date with the latest software versions as well(assuming anything changed)

[Baldrick]

updated the easycd and nero guides.