github: Package source: github
In hadley/packman:

Package source: github

1 2	github(username = "hadley", repo = NULL, ref = "master", subdir = NULL, auth_user = NULL, password = NULL)

`username`	This is the only parameter that must be specified, and for the recommended package structure on github it is the only parameter that should be specified
`repo`	The repo name - if ommited, the package name is used
`ref`	The branch/tag name to use - if omitted, will look in master, and in all appropriately named tags
`subdir`	If the package is not found in the root directory of the package this specifies where it should be found.
`auth_user`	If authentication is needed, and the authentication username is different to the `username`
`password`	The password to use for authentication

h <- github("hadley")
has_package(h, "ggplot2")
has_package(h, "ggplot3")
package_info(h, "ggplot2")

w <- github("wch")
has_package(w, "extrafont")
has_package(c(h, w), "extrafont")