This CLI will teach us what name a shogun or a regent in the Kamakura shogunate is.
$ go get github.com/jyouj/go-kamakura
If you input only a number, this CLI will show the shogun's name.
$ go-kamakura 3
源実朝
If you input a number with the option, this CLI will show the regent's name.
$ go-kamakura -s 3
北条泰時