Create package specification list which consists of all the details required to identify and acquire source of the package.
package_spec(name = NULL, repos = NULL)package_spec_source(path = NULL, ...)
package_spec_archive_source(path = NULL, ...)
name of the package.
repository where package with given name should identified.
path to the source of the package (either bundled or not). URLs are acceptable.
parameters passed to downstream constructors