Revert "Remove rbenv binary, swtich to boxen"

This reverts commit 23af097d6b20d89df3270119619012f2621e27af.
Revert "Add boxen configuration"

This reverts commit 151f7e90467d5ab6b3710761e1675a855f166d5d.

Conflicts:
	zshrc
Incorporate bin/setup to bin/bootstrap, run bin/dotfiles from bootstrap, ...