Consistently omit normalization for quaternions.

[tkoolen]

The main reason for this is to provide better support for scalar types for which square root or division are not defined.

[codecov-io]

Codecov Report

Merging #514 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #514   +/-   ##
=======================================
  Coverage   99.23%   99.23%           
=======================================
  Files          38       38           
  Lines        1700     1700           
=======================================
  Hits         1687     1687           
  Misses         13       13

Impacted Files	Coverage Δ
src/joint_types/quaternion_spherical.jl	100% <ø> (ø)	⬆️
src/joint_types/quaternion_floating.jl	100% <ø> (ø)	⬆️

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