Imply Marathon 1 & Marathon 2 -> Marathon_(series)

BUR #61002 is pending approval.

create implication marathon_(1994) -> marathon_(series)
create implication marathon_2:_durandal -> marathon_(series)

I doubt having the first two Marathon games imply Marathon (series) will be terribly controversial.
In hindsight, maybe the original game's tag should have been Marathon 1, even if the site's game tags aren't entirely consistent there.