optimize dependencies

[Adafede]

Hi @fmichonneau!

Thank you for your handy package!

I am using it in mine (https://github.com/taxonomicallyinformedannotation/tima-r) and I saw it comes with quite heavy dependencies.

I did a quick

library(pkgndep)
x = pkgndep("rotl")
dependency_report(x)

and it looks like many of those only come from your unused suggestions (phylobase, RNeXML, ...) this could save already 40 unnecessary dependencies 😮
A lot (12) is only because of your read_nexus_phylo function from your other package but this is used, so probably less easy to avoid.

Nothing important, I just discovered the useful tool from @jokergoo myself so wanted to share it!

Best,