Add Hirakata plugin based on hiragana-katakana-zshprompt

I made a plugin based on [hiragana-katakana-prompt](https://github.com/Mawu3n4/hiragana-katakana-zshprompt/blob/master/README.md), it let you add a random Japanese character in your prompt and it will also play the sounds of it.

The character changes after every command (using zsh builtin fonction `precmd()`)

The plugin is created for people willing to learn Japanese and memorize the characters easily.