Repository address in the format
username/repo[/subdir][@ref|#pull]. Alternatively, you can
specify subdir and/or ref using the respective parameters
(see below); if both is specified, the values in repo
username
User name. Deprecated: please include username in the
repo
ref
Desired git reference; culd be a commit, tag, or branch name.
Defaults to master.
subdir
subdirectory within repo that contains the R package.
auth_user
your account username if you're attempting to install
a package hosted in a private repository (and your username is different
to username)