Revise vignettes based on Wickham book

[xiangzhu]

Below is a check list of guidelines on files in vignette / from Wickham's package book: http://r-pkgs.had.co.nz/vignettes.html.

This part seems straightforward since the main tools are rmarkdown and knitr, with which I have some experiences. However, preparing and organizing the contents of vignettes may be as hard as writing articles.

• Start with devtools::use_vignette("my-vignette").
• Can build all vignettes from the console with devtools::build_vignettes(), but this is rarely useful. Instead use devtools::build() to create a package bundle with the vignettes included.
• Need to put yourself in the readers’ shoes, and adopt a “beginner’s mind”.
• Any packages used by the vignette must be declared in the DESCRIPTION.
• Need to watch the file size.