Eigen transforms

[ZackAttack614]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 39.63%. Comparing base (c1fbb97) to head (f3297f0).
Report is 27 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #744      +/-   ##
==========================================
- Coverage   39.70%   39.63%   -0.07%     
==========================================
  Files         135      140       +5     
  Lines       22392    22697     +305     
==========================================
+ Hits         8890     8997     +107     
- Misses      13502    13700     +198     

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[kpwelsh]

A couple of minor things should be changed.
A couple of minor things could be changed.

Not 100% sure if there is a better way to do the xsimd or not.

[psavery]

I ran a quick performance check on running hexrd fit-grains ./mruby_config_composite.yml, and after these changes, it took 139 seconds instead of 141.5 seconds before. It's about the same speed - which is good!