check in pkg

pkg is a python script for making symbolic link for a software package

e.g. A software package located at /usr/local/FOO
which contains bin/bar

Running ./pkg link /usr/local/FOO
it will do ln -s /usr/local/FOO/bin/bar /usr/local/bin/bar

Running ./pkg unlink /usr/local/FOO
it will do rm /usr/local/bin/bar