To do

[moble]

Implement and test:

• Add and test frules
• Add r/frules for log, sqrt, etc. Maybe squad and slerp?
• axis-angle converters
• Find more precise conversion to spherical coordinates. Note that acos is not a stable approach.
• distance
  • intrinsic rotor
  • intrinsic rotation
  • chordal rotor
  • chordal rotation
• Subtypes
  • Use AbstractQuaternion everywhere possible
  • Add Rotor type (or maybe UnitQuaternion)
  • Add Vec type
  • Specialize functions to work with them — especially exp, log, and sqrt
  • Extend wrapper to take an op argument along with two types, and return the appropriate wrapper type
  • Look at every function and consider every combination of types
  • Test new types and combinations
• interpolation
  • squad
  • slerp
  • unflip rotors
• time series
  • from_angular_velocity
  • to_angular_velocity
  • minimal rotation
• Add conjugate function to efficiently rotate vectors by rotors
• Reduce direct dependencies using extensions, with backwards compatibility via Requires
• Simplify quaternion.jl
  • Remove parameters wherever possible
  • Add quaternion, rotor, and quatvec functions
    • Use rotor(...; normalize=false)
    • Accept arbitrary arrays, and return arrays of the corresponding type
    • Accept type parameter as optional argument or keyword argument, with default as detection