Use besselix instead of besseli for better numerical stability.

[marcpabst]

This PR improves numerical stability for the von-Mises-Fisher distribution for large values of κ.

[marcpabst]

Will do!

[codecov-commenter]

Codecov Report

Base: 85.94% // Head: 85.94% // No change to project coverage :thumbsup:

Coverage data is based on head (6f8536e) compared to base (5566488). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1598   +/-   ##
=======================================
  Coverage   85.94%   85.94%           
=======================================
  Files         129      129           
  Lines        8083     8083           
=======================================
  Hits         6947     6947           
  Misses       1136     1136           

Impacted Files	Coverage Δ
src/multivariate/vonmisesfisher.jl	93.33% <100.00%> (ø)

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[marcpabst]

Okay, I hope tests are okay now?

[marcpabst]

I think the one failing test is unrelated to my changes?

[devmotion]

Thank you for the PR!

I wanted to add these improvements, so I applied the suggestions and hope this is fine with you.