Add gtools for R

[leechaowen]

Please complete the following information about the package:

• Package name:gtools
• Language name:R
• Website:https://CRAN.R-project.org/package=gtools

Following are optional, but will help us consider adding:

• Why is this useful?
• Example Code:

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:+1: reaction might help to get this request prioritized.

[leechaowen]

R environment currently has little packages installed. it's better install all packages from CRAN. https://cran.r-project.org/ It's crazy to request install packages one by one