Fixes #856
Fixes #857

The bug is as follows:

    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 && echo yes || echo no'
    yes
    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 $ZSH_VERSION && echo yes || echo no'
    yes

This commit deploys the following workaround:

    % zsh-5.8 -fc 'autoload is-at-least; is-at-least 5.8.0.2 $ZSH_VERSION.0.0 && echo yes || echo no'
    no

Fixes #756.

This reverts commit 8a1bd7c8b6.

The detection only works correctly from a widget function, so the change
was wrong: it caused zsh_highlight__memo_feature to be set to false
every time.

Fixes #579 (zsh-autosuggestions interoperability).
Fixes #735 (ditto).

See https://github.com/zsh-users/zsh-syntax-highlighting/issues/579#issuecomment-650126055
See https://github.com/zsh-users/zsh-autosuggestions/issues/529#issuecomment-650481227

This is needed for feature/redrawhook to be able to use it.

Fixes #418 (interoperability issue with other plugins).

Without this patch, `_zsh_highlight` was invoked by add-zle-hook-widget
with `$?` being non-zero (see add-zle-hook-widget:48-52).  Since
`_zsh_highlight` preserves `$?` from its caller's point of view,
add-zle-hook-widget saw a non-zero exit code from `_zsh_highlight` and
did not run any the remaining zle-line-pre-redraw hooks.

See https://github.com/zsh-users/zsh-syntax-highlighting/issues/579#issuecomment-623576907.

Fixes #719.

Cf. #688.

The «emulate» call isn't sufficient, since these lines are parsed before
it takes effect.

Fixes #689 (née #622).

See also #688 for preventing these gymnastics from being needed in the
first place.

See also https://github.com/junegunn/fzf/pull/1924 for an inter-plugin
interaction that this probably fixes.

./.editorconfig is already set correctly.

Fixes #612.

This avoids a bug in zsh 4.3.12 and prior which affects passing
arguments to an anonymous function.

Found-by: Matthew Martin

Suggested-by: m0viefreak

Based on code by Bart Schaefer (reference within).

Tested with zsh 5.0.7-5 (debian package) and with 5b4cbcc842c6 (39158,
5.3-to-be of today).

(Currently a noop)

Compare issue #288.

This feature will be released in zsh 5.3.  Older zsh's will use the existing
codepath.

zsh/macOS bug: http://www.zsh.org/cgi-bin/mla/redirect?WORKERNUMBER=42891

Fixes #449.