Remove plyr dependencies

[srvanderplas]

Issue 70 discusses removing plyr from the dependency list. I have gone through the functions and removed plyr-based functions, replacing them with purrr where possible. In the case of plyr::rename, I have added the rename function code from plyr under the name rename_plyr - the functionality wasn't easily matched using the dplyr equivalent, but that one dependency doesn't justify importing the entire plyr package, so I did as suggested in Hadley's R Packages book and duplicated the function.

[dahtah]

Hi - thanks for doing this, it's really welcome. Why did you close the PR, though?

[srvanderplas]

I found another instance I'd missed and didn't have time to fix it just then. I will try to get to it tomorrow 😊.

On Sun, Jun 2, 2019, 03:42 Simon Barthelmé notifications@github.com wrote:

Reopened #98 https://github.com/dahtah/imager/pull/98.

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[srvanderplas]

Ok, Travis is passing now, so let me know if there's anything else that you need me to fix!

[Bisaloo]

Thanks a bunch @srvanderplas for your work on this and @dahtah for review and merging! This is awesome!