SubcultureWaterFallクラスを実装

```python
> python
Python 2.7.8 (default, Oct 17 2014, 05:09:33)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.51)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = [u'b', u'c']
>>> a
[u'b', u'c']
>>> '\n'.join(a)
u'b\nc'
>>>
```