There is a current bug where horses that spawn with certain speed to end up being extremely fast in moving, and thus can keep moving never ever stopping.(When no one is on them)
This ofcourse is not good in any way.
This update adds a killall and kill command
horse killall will allow all horses that are spawned via this plugin to be removed without dropping its items so they disappear, their health isn't set to 0.
horse kill will eliminate the horse you are riding at that moment.