R: Implement Download Buttons in 'rmarkdown'

# Implement Download Buttons in 'rmarkdown'

## Documentation for package ‘downloadthis’ version 0.5.0

- DESCRIPTION file
- User guides, package vignettes and other documentation
- Package NEWS
- Package README

## Help Pages

download_dir | Download a directory
download_file | Download a local file or multiple files
download_link | Download file from a web address
download_this | Download data frames, lists, or any R object