Add support for higher dimensional rotation

[hyrodium]

This PR fixes #215.

• [x] RotMatrix{N} constructor
• [x] RotMatrixGenerator{N} constructor
• [x] exp function RotMatrixGenerator{N} to RotMatrix{N}
• [x] log function RotMatrix{N} to RotMatrixGenerator{N}
• [x] isrotationgenerator function
• [ ] ~rotation_angle~
• [x] rand method
• [x] documentation

[hyrodium]

The CI log says:

Testing isrotation: Error During Test at /home/runner/work/Rotations.jl/Rotations.jl/test/rotation_tests.jl:439
  Test threw exception
  Expression: isrotation(I(1))
  MethodError: objects of type UniformScaling{Bool} are not callable
  Stacktrace:
   [1] macro expansion at /home/runner/work/Rotations.jl/Rotations.jl/test/rotation_tests.jl:439 [inlined]
   [2] macro expansion at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/Test/src/Test.jl:1083 [inlined]
   [3] macro expansion at /home/runner/work/Rotations.jl/Rotations.jl/test/rotation_tests.jl:407 [inlined]
   [4] macro expansion at /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.0/Test/src/Test.jl:1083 [inlined]
   [5] top-level scope at /home/runner/work/Rotations.jl/Rotations.jl/test/rotation_tests.jl:89

Like https://github.com/JuliaArrays/StaticArrays.jl/pull/985, we can drop support under Julia v1.6.

[codecov[bot]]

Codecov Report

Merging #219 (9294916) into master (4f76c5a) will increase coverage by 0.41%. The diff coverage is 98.82%.

@@            Coverage Diff             @@
##           master     #219      +/-   ##
==========================================
+ Coverage   88.14%   88.56%   +0.41%     
==========================================
  Files          15       16       +1     
  Lines        1603     1626      +23     
==========================================
+ Hits         1413     1440      +27     
+ Misses        190      186       -4     

Impacted Files	Coverage Δ
src/euler_types.jl	92.25% <ø> (-0.18%)	:arrow_down:
src/mrps.jl	34.93% <ø> (-0.88%)	:arrow_down:
src/rodrigues_params.jl	98.64% <ø> (-0.04%)	:arrow_down:
src/unitquaternion.jl	96.36% <ø> (-0.04%)	:arrow_down:
src/logexp.jl	93.33% <93.33%> (+11.51%)	:arrow_up:
src/core_types.jl	94.81% <100.00%> (+0.65%)	:arrow_up:
src/rand.jl	100.00% <100.00%> (ø)
src/rotation_generator.jl	96.35% <100.00%> (+0.44%)	:arrow_up:

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[hyrodium]

Thanks for the review! I have added a TODO list in the description.

[hyrodium]

I was misunderstanding the rotation angle of highter dimensional rotation, and I have reverted the rotation_angle for highter dimensional rotation. I thought a rotation have one rotation angle, but that was incorrect; in general, a n-dimensional rotation has n÷2 rotation angles. See https://cs.brynmawr.edu/~dxu/206-2550-2.pdf for more information.

[hyrodium]

I have added documentation, and I think this is ready to merge.