If you refer to the previous commit where I change shell-command usages to
start-process function calls, you'll see the rationale for why I prefer
start-process.
This commit introduces a more ergonomic API for start-process that fits most of
my current use-cases of it. This cleans up the code. I have introduced a bug in
the way that I'm tokenizing the COMMAND value. I've tracked that with a
TODO. For now it only affects the `xmodmap -e '<command-string>'` calls, which
isn't too disruptive.
5785a5d126