Yuto Horikawa

This PR also fixes `setindex` for non-square matrix **Before this PR** ```julia julia> a = ones(3,3) 3×3 Matrix{Float64}: 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 julia> Base.setindex(a,0.0,3,2) 3×3...

>That would be fine. If someone defines an rrule to delete these that's probably a better option. But I don't think we should merge something that we know is going...

>One example is trying to do Zygote over a code like https://github.com/JuliaDiff/FiniteDiff.jl/blob/cfee15e33394067f883fb685ea9f305d0bce9f0f/src/jacobians.jl#L196 . I have tested [FiniteDiff/test/runtests.jl](https://github.com/JuliaDiff/FiniteDiff.jl/blob/master/test/runtests.jl) with changes in this PR in my local PC, but the test didn't...

I just rebased to the current `master` branch yesterday. I'm waiting for approval to run the workflows.

Is there any good place to find example documentation? I thought [JuliaHub](https://juliahub.com/ui/Packages) would be a good place to find packages and documentations, but the most of documentations are deployed on...

x-ref https://github.com/JuliaDiff/DualNumbers.jl/issues/45

>So it's confusing that two `UnitQuaternion`s can be `==` but have different values of the field: `q == -q` but `q.w != (-q).w`. I think the `==` operator here is...

>but the other Rotation types seem to fit the description "can be converted to a `RotMatrix`," rather than "is a matrix." WDYT? Indeed, but I think the relation between `RotMatrix{3}

>One way to improve this i.m.o. would be to rename `UnitQuaternion` to something like `QuatRotation`. I totally agree with that. Or maybe `VersorRotation`? I just found out the word "versor"...

Great! I didn't know that the `Unitful` works exactly. ```julia julia> import Unitful.° julia> sin(30°) 0.5 julia> sin(π/6) 0.49999999999999994 ```