theme: add kanagawa

[Anskrevy]

This theme is based on rebelot's theme by the same name. I've never written a theme before and still pretty new to using emacs so please let me know if I've missed something/something doesn't look right.

Fixes #0000 References #0000 Replaces #0000

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• [X] I searched the issue tracker and this hasn't been PRed before.
• [X] My changes are not on the do-not-PR list for this project.
• [X] My commits conform to the git conventions.
• [X] My changes are visual; I've included before and after screenshots.
• [ ] I am blindly checking these off.
• [X] Any relevant issues or PRs have been linked to.
• [ ] This a draft PR; I need more time to finish it.

Screenshots

[azzamsa]

Is anything else needed for this PR to merge into the master? I am here to help.

[NU11V01D]

Anything left for the theme to be merged?

[Anskrevy]

Since I opened this pull request, reblot has released an official kanagawa wave theme for Emacs. I've been working on porting the three main themes but they are rather different from the one in this PR, which is a hybrid of the wave and dragon themes. Here are some screenshots of the new themes.

wave

dragon

lotus

abyss (the hybrid)

Since this has not been merged, would it be best to include these themes in this PR, or open a new PR for the three original themes and rebrand this one?

[NU11V01D]

I'd include rebelot's here and name differently the custom variations. Wave, Lotus and Dragon would be the originals and the other variations would be up to you.

[Anskrevy]

Sounds good. All the necessary changes have been made. Let me know if there are any issues.