Add japanese_zodiac option to Eto.name / eto name command

# 十干十二支を取得可能にするオプションを追加
## Eto.name(year,  japanese_zodiac = true)

~~~ruby
require 'eto'

Eto.name(1965) # => "巳"
Eto.name(1965, true) # => "巳"
Eto.name(1965, false) # => "乙巳"
Eto.name(1977) # => "巳"
Eto.name(1977, true) # => "巳"
Eto.name(1977, false) # => "丁巳"
~~~

## eto name <year> --no-japanese_zodiac

~~~bash
$ eto name 1977
巳
$ eto name 1978
午
$ eto name 1965 --not-japanese_zodiac
丁巳
$ eto name 1977 --not-japanese_zodiac
乙巳
# alias
$ eto name 1965 --njz
乙巳
~~~