Handling the `!`s on the public_suffix_list dataset

[alexcpsec]

With this on the dataset:

// jp geographic type names
// http://jprs.jp/doc/rule/saisoku-1.html
*.kawasaki.jp
*.kitakyushu.jp
*.kobe.jp
*.nagoya.jp
*.sapporo.jp
*.sendai.jp
*.yokohama.jp
!city.kawasaki.jp
!city.kitakyushu.jp
!city.kobe.jp
!city.nagoya.jp
!city.sapporo.jp
!city.sendai.jp
!city.yokohama.jp

This is incorrect:

> suffix_extract("city.sapporo.jp")
             host subdomain domain          suffix
1 city.sapporo.jp      <NA>   <NA> city.sapporo.jp

Not sure what the "right" is right now.

[alexcpsec]

I take this back. We don't need this for out current use.