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

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devmotion merged 6 commits intoJuliaMath:masterfrom

devmotion:dw/besselx

Oct 18, 2021

Commits on Sep 28, 2021

Commits on Oct 1, 2021

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

Commits on Oct 2, 2021

Improve `frule`s
devmotion
committed

Commits on Oct 3, 2021

Simplify `frule`s
devmotion
authored

Commits on Oct 4, 2021

Apply suggestions from code review

devmotion
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sethaxen
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