Have some way to specify dependency scripts

It took me some time to fully grasp the difference of philosophy between install and dot.

dot runs as the last step of bootstrap and makes sure that all dependencies get installed. install depends on things that will be installed with dot, such as homebrew, python or cask.

I would like dot to run all dependency-install scripts like those and avoiding them to be run with install. A good naming could be install-dep.sh.