Fixes #585.

Closes #607 #649 #704

The fix is to exempt such aliases from the empty commands sanity check.

The great-grandparent commit, "a3ae74 'main': Fix the last commit's bug
concerning parameter elision not happening in redirects in command
position.", is not added because it's not a change with respect
to 0.7.1.

In those versions of zsh, «[[ -o nosuchoption ]]» is regarded as
a syntax error.  In newer zsh versions, it merely returns non-zero
(specifically, it returns 3, unlike «[[ -o unsetoption ]]» which
returns 1).

Fixes #732.
Fixes #733.

Fixes #461.

Fixes #430.

This is not perfect: we don't try to detect cases such as «$((ls); (ls))»,
which look like arithmetic expansions but are in fact command substitutions.

Fixes part of #607.

Introduces #704.

Fixes #694.

Fixes #583.

Fixes #582.

Fixes #676.

- Move an entry to another section.
- Fix commit hash width.
- Add missing punctuation.