Refactor into a series of independent programs

Each subshell now manages when it should run on its own and the
organization and ordering is much more coarse-grained.

Additionally, the Mac now manages its crontab!
Touch ~/.ssh-agent-expiry before SSHing

This is the other half of the cron job that proactively empties the SSH
agent after 10 minutes of inactivity.  Right now that job's dependent on
~/.profile.d/ssh.sh but that'll soon not be the case.

Unfortonately, this loses the LXC madness I had in my home directory for
years.  History's what Git's for, though.
Minor tweaks for Linux