more power packages

[mattansb]

https://cran.r-project.org/web/packages/pwr
https://cran.r-project.org/web/packages/pwrss
https://cran.r-project.org/web/packages/pwr2ppl
https://cran.r-project.org/web/packages/WebPower
https://cran.r-project.org/web/packages/Superpower
https://cran.r-project.org/web/packages/TrialSize
https://cran.r-project.org/web/packages/mlpwr