Add derivatives for `besselix`, `besseljx`, and `besselyx`#350

Merged

devmotion merged 6 commits intoJuliaMath:masterfrom devmotion:dw/besselx

Oct 18, 2021

+100-1

Commits on Sep 28, 2021

Commits on Oct 1, 2021

Apply suggestions from @sethaxen 's review (muladd + optimizations)
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committed

Commits on Oct 2, 2021

Improve frules
devmotion
committed

Commits on Oct 3, 2021

Simplify frules
devmotion
authored

Commits on Oct 4, 2021

Apply suggestions from code review

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sethaxen
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