Code quality/refactor

[mgree]

We should:

• [ ] Unify error reporting and debug output
• [ ] Normalize style (variable names, quoting, indentation, ; use)
• [ ] Clarify dependencies, distinguishing between dev/testing dependencies (e.g., expect) and runtime dependencies
• [ ] Ensure that mergerfs is optional/produces a legible error when we need it and it's not there
• [ ] #72
• [ ] #76
• [x] #45
• [ ] Clean up testing infrastructure (see #66 for some initial directions)
• [ ] Have CI confirm the version in the manpage matches the script

[angelhof]

Great list!

[a1346054]

Consider using shfmt to unify the codestyle across the scripts, and perhaps enforcing it in CI.

Consider picking some shell styleguide for the project, such as https://google.github.io/styleguide/shellguide.html