Kata/Katas: defining the plural to use in the docs

[Blind4Basics]

I noticed I use "Katas" while hobovsky use "Kata" as plural. Unnamed already talked about that too.

We should always use the same way throughout the whole documentation, so which one will it be?

[kazk]

Kata

Japanese words are not inflected for plural and it’s awkward to see as a Japanese. So I’d prefer kata, kumite, kyu, and dan not inflected in the documentation.

[Blind4Basics]

Done.

edit: I forgot to check for kumite... I'll do another pass.

edit²: checked, all good.