rename UnitQuaternion to QuatRotation

[hyrodium]

As discussed in #171 (comment), UnitQuaternion is confusing, and should be renamed to QuatRotation.

[codecov]

Codecov Report

Merging #201 (671ad49) into master (2e02102) will not change coverage.
The diff coverage is 93.10%.

@@           Coverage Diff           @@
##           master     #201   +/-   ##
=======================================
  Coverage   86.74%   86.74%           
=======================================
  Files          14       14           
  Lines        1403     1403           
=======================================
  Hits         1217     1217           
  Misses        186      186           

Impacted Files	Coverage Δ
src/mean.jl	0.00% <0.00%> (ø)
src/mrps.jl	35.37% <87.50%> (ø)
src/rodrigues_params.jl	98.66% <87.50%> (ø)
src/error_maps.jl	93.19% <88.23%> (ø)
src/unitquaternion.jl	96.20% <97.61%> (ø)
src/angleaxis_types.jl	94.05% <100.00%> (ø)
src/core_types.jl	90.44% <100.00%> (ø)
src/derivatives.jl	100.00% <100.00%> (ø)
src/principal_value.jl	100.00% <100.00%> (ø)
src/rotation_error.jl	82.60% <100.00%> (ø)

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[c42f]

Looks good to me.

[c42f]

You can probably remove this old deprecation.

[hyrodium]

Can I remove RodriguesVec and SPQuat too?

The old deprecations for RodriguesVec, SPQuat and Quat has been introduced in this commit (#116):
793d384#diff-0c3a3096ea8aa5548f7facdd7eaa649293a64f785376cca25e23f14d6af4301d

If we can remove the deprecation for Quat, then I think the others also can be removed.
The old type names were already deprecated before v1.0.0 release, so I thought it's okay to remove them.

[c42f]

Sure, sounds fine.