(mere non-use of easement insufficient to terminate easement; owner erected fence in middle of driveway easement, constructed barn at end of easement, never spread gravel to indicate driveway; neighbor planted trees and mowed grass up to fence of easement for period of more than 15 years; court held fence and barn construction established owners abandonment of easement and neighbor’s acquired their portion of easement by adverse possession through continued use of their side of easement; affirmed on appeal).