pkg_branch(), the package name is obtained from the environment
variable TRAVIS_BRANCH; if it is empty, the current GIT branch name is
used, and the branch name must be of the form pkg/name, i.e. the
package name with the pkg/ prefix.For pkg_commit(), the package named is detected from the
current commit message, which should contain a character string of the form
[crandalf pkg@user/repo], where user/repo is a repository on
Github.
pkg_branch()
pkg_commit()NULL if failed to find one.