This package was originally created by Stephane Champely, from the University of Lyon. The official release of the package is on CRAN: http://cran.r-project.org/web/packages/pwr/
To get this package with extended intervals fix (e.g., for sample sensitivity analysis) installed instead, just write in an R session:
library(devtools)
install_github("SvenHeim-UDE/pwr")
After installing, you have to load to use the package, with:
library(pwr)
Feel free to comment on any issues, file bugs or suggest improvements. All contributions are welcome!