jeremyong/klein: v2.1

This version adds a number of QoL improvements as well as improvements to precision for a nominal cycle cost:

1. The kln::sqrt free function is available and accepts as its argument kln::rotor, kln::branch, kln::translator, and kln::motor. The function returns the quantity x such that x*x is equal to the argument to within a good approximation.
2. Motors can now be multiplied by rotors and translators to produce new motors containing the composite action. This was an oversight from the existing API.
3. Line normalization now correctly stays on the Lie manifold.
4. Additional helper routines have been added to compute rcp, sqrt, and rsqrt to ~22 bits of accuracy.