added comments on the two main trail data structures
added comments on the two main trail data structures

vinh3928/trailsy,mgraesser/trailsy,vinh3928/trailsy,CodeForBoulder/trailsy,remory08/trailsy,JamesGould123/trailsy,JamesGould123/trailsy,CodeForBoulder/trailsy,trevorackerman/trailsy,remory08/trailsy,mgraesser/trailsy,mbarrenecheajr/trailsy,mbarrenecheajr/trailsy,trevorackerman/trailsy