======== no ability to 'source' another file ========

This varies greatly by file type.  If a file doesn't have the ability to 'source' another file,
then I'm greatly hampered by how much computer-specific-tailoring I can do.


- ~/.ssh/config
            (I'd like to keep my work and public settings in separate repos; I'd also like to have
             per-machine-customizations)

             A possible solution, however, is:  https://github.com/dbrady/ssh-config

- ~/.gitconfig
            (I'd like to keep my work and public settings in separate repos)
            (also, the 'github.token' setting needs to be stored in a private repo)

            A possible solution, however, is running a series of 'git config --global' commands
            every time you run ~/setup.pl