Add martial arts books to libraries

[SzQ1]

Because I think they are not on the spawn list. I will do that later.

[Coolthulhu]

Should be rare drops.
Might be worth adding to mansions as well.

[SzQ1]

Well right now they are barely to be found, still should be possible to spawn in libraries, rare but possible.

[Dreamer1]

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[pengwu26]

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[Krwak]

I second this.
Maybe make it that you can't learn all the martial arts in the world from books but being able to find them would be nice.
Or make it that you can only swap between three different martial arts at a time that you have to 'prepare' before going to sleep or after sleeping and not being able to change otherwise.