>>> tower = Towers(height=3)
    >>> print(tower)
    Towers(Rods(3 - start([***, **, *]), end([]), tmp([])))

    >>> print('moves required: {moves}'.format(moves=tower.moves_for_height(height)))
    moves required: 7

    >>> with tower:
    ...    for i in tower:
    ...        print(i)
    Move(disk=*, start=Rod(name='start', disks=[***, **, *], height=3), end=Rod(name='end', disks=[], height=3), moves=0)
    Move(disk=**, start=Rod(name='start', disks=[***, **], height=3), end=Rod(name='tmp', disks=[], height=3), moves=1)
    Move(disk=*, start=Rod(name='end', disks=[*], height=3), end=Rod(name='tmp', disks=[**], height=3), moves=2)
    Move(disk=***, start=Rod(name='start', disks=[***], height=3), end=Rod(name='end', disks=[], height=3), moves=3)
    Move(disk=*, start=Rod(name='tmp', disks=[**, *], height=3), end=Rod(name='start', disks=[], height=3), moves=4)
    Move(disk=**, start=Rod(name='tmp', disks=[**], height=3), end=Rod(name='end', disks=[***], height=3), moves=5)
    Move(disk=*, start=Rod(name='start', disks=[*], height=3), end=Rod(name='end', disks=[***, **], height=3), moves=6)

    >>> print(tower)
    Towers(Rods(3 - start([]), end([***, **, *]), tmp([])))

    >>> print('moves taken: {moves}'.format(moves=tower.moves))
    moves taken: 7