Request for 2 libraries please

[kgdunn]

I've integrated DataCamp-Light in several places in my online textbook, https://learnche.org/pid and highly recommend DataCamp in general whenever I can, and also in my MOOC on Experimentation for Improvement.

However, two R libraries would help greatly: the 'robust' library, and the 'pid' library. The latter is small, and would be really helpful to include please.

Thanks, Kevin.