Fix inefficient implementation of boot.bruvo

[StaffanBetner]

Please place an "x" in all the boxes that apply

• [x] I have the most recent version of poppr and R
• [ ] I have found a bug
  • [ ] I have searched for solutions on this site and the poppr forum
  • [ ] I have a reproducible example
• [x] I want to request a new feature

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I have found that boot.bruvo is very inefficiently implemented. It would be a better approach to store the distance matrices per locus, and sample them with replacement, and then calculate trees, instead of recalculating the distance matrices for every iteration.

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[zkamvar]

Would you be willing to submit a PR for this?

[StaffanBetner]

I only have some very ugly code that remedies this problem, but I will at least look into it. I suspect there are other speed improvments as well that can be done.

[zkamvar]

Thank you. For the record, with the advent of {styler}, ugly code is not much of a problem. For contributions, I require that they are formally tested.