Aliases that should be removed

[okamsn]

We want to pare down the documentation and complexity. Some commands just have too many names.

• [x] group for command-do. This isn't a meaningful name.
• [ ] finally-protected for finally-protect? The special form is unwind-protect, so we should match that, but Iterate uses finally-protected.
• [x] prev-set, prev-expr, and prev for set-prev.
  • We have a theme with set, set-prev, and set-accum.
  • prev is too generic.
• [x] expr and exprs for set? Like above, we should use a consistent theme.
• [x] num and nums for numbers and the up and down variants.

[okamsn]

We've decided not to remove finally-protected, since it is also used by Iterate.

[okamsn]

Closed via #207.