set up renv in this project

[egnor]

I don't know what you think about renv but I find it absolutely invaluable for library development, to avoid depending on a global R environment and its unpredictable contents.

(If you're not into it, then I'll just use it locally! Maybe you'd let me at least add its files to .gitignore in that case.)

[egnor]

Added a reference to bunny (and improved the .Rprofile logic to be more robust) to fix #28

[jcpsantiago]

I use it on all my projects actually, but usually skip it for libraries (I added it to some though). I don't see any problems with adding it. Thanks!

I'm waiting for this repo to be transfered to my personal account, I'll merge this as soon as that happens (ETA today or tomorrow)

[egnor]

CI failures --

MacOS: This looks unrelated to this change?? Maybe related to the old setup-r@v1 action?

Ubuntu (both versions): This is definitely related to this change, strange how it's not able to use the Remotes:? Looking into that.

[egnor]

Running rcmdcheck in my local environment works fine:

Again, maybe an issue with the older versions of the R workflow actions?

[jcpsantiago]

@egnor I think so, they haven't been updated in aaages... something TODO, especially now that there's commit activity again (thanks for that BTW :) )