Update modus-themes to version 1.5.0

Update modus-themes to version 1.5.0

* doc/misc/modus-themes.org (Enable and load): Include internal link.
(Sample configuration for use-package): Update code sample.
(Customization Options): Update references to customization options.
(Option for more italic constructs): Document new variable, as an
alias of the deprecated 'modus-themes-slanted-constructs'.

(Option for syntax highlighting, Option for links)
(Option for command prompt styles, Option for mode line presentation)
(Option for language checkers)
(Option for line highlighting (hl-line-mode))
(Option for parenthesis matching (show-paren-mode))
(Option for active region, Option for the headings' overall style):
Update documentation to describe new possible values, expressed as a
list of symbols.

(Option for Org agenda constructs): Document new user option.

(Control the scale of headings): Update symbol of variable.

(Remap face with local value (DIY), Backdrop for pdf-tools (DIY)):
Tweak text of internal reference.

(Font configurations for Org and others (DIY)):  Add internal link and
document how to configure the 'bold' and 'italic' faces.

(Custom Org user faces (DIY)): Minor corrections or changes to single
words.

(Full support for packages or face groups): Include new items.

(Notes on individual packages): Add notes on Avy hints, the colour of
days in 'M-x calendar', and underlines in 'compilation-mode' buffers.

(What is the best setup for legibility?): Remove single word.
(Acknowledgements): Update list of contributors.

* etc/themes/modus-themes.el (modus-themes-faces)
(modus-themes-operandi-colors, modus-themes-vivendi-colors)
(modus-themes-subtle-red, modus-themes-subtle-green)
(modus-themes-subtle-yellow, modus-themes-subtle-blue)
(modus-themes-subtle-magenta, modus-themes-subtle-cyan)
(modus-themes-subtle-neutral, modus-themes-intense-red)
(modus-themes-intense-green, modus-themes-intense-yellow)
(modus-themes-intense-blue, modus-themes-intense-magenta)
(modus-themes-intense-cyan, modus-themes-intense-neutral)
(modus-themes-refine-red, modus-themes-refine-green)
(modus-themes-refine-yellow, modus-themes-refine-blue)
(modus-themes-refine-magenta, modus-themes-refine-cyan)
(modus-themes-active-red, modus-themes-active-green)
(modus-themes-active-yellow, modus-themes-active-blue)
(modus-themes-active-magenta, modus-themes-active-cyan)
(modus-themes-fringe-red, modus-themes-fringe-green)
(modus-themes-fringe-yellow, modus-themes-fringe-blue)
(modus-themes-fringe-magenta, modus-themes-fringe-cyan)
(modus-themes-nuanced-red, modus-themes-nuanced-green)
(modus-themes-nuanced-yellow, modus-themes-nuanced-blue)
(modus-themes-nuanced-magenta, modus-themes-nuanced-cyan)
(modus-themes-special-cold, modus-themes-special-mild)
(modus-themes-special-warm, modus-themes-special-calm)
(modus-themes-diff-added, modus-themes-diff-changed)
(modus-themes-diff-removed, modus-themes-diff-refine-added)
(modus-themes-diff-refine-changed, modus-themes-diff-refine-removed)
(modus-themes-diff-focus-added, modus-themes-diff-focus-changed)
(modus-themes-diff-focus-removed, modus-themes-diff-heading)
(modus-themes-pseudo-header, modus-themes-mark-alt)
(modus-themes-mark-del, modus-themes-mark-sel, modus-themes-mark-symbol)
(modus-themes-heading-1, modus-themes-heading-2, modus-themes-heading-3)
(modus-themes-heading-4, modus-themes-heading-5, modus-themes-heading-6)
(modus-themes-heading-7, modus-themes-heading-8, modus-themes-hl-line)
(modus-themes-bold, modus-themes-slant, modus-themes-variable-pitch)
(modus-themes-graph-red-0, modus-themes-graph-red-1)
(modus-themes-graph-green-0, modus-themes-graph-green-1)
(modus-themes-graph-yellow-0, modus-themes-graph-yellow-1)
(modus-themes-graph-blue-0, modus-themes-graph-blue-1)
(modus-themes-graph-magenta-0, modus-themes-graph-magenta-1)
(modus-themes-graph-cyan-0, modus-themes-graph-cyan-1)
(modus-themes-lang-note, modus-themes-lang-warning)
(modus-themes-lang-error, modus-themes-reset-soft)
(modus-themes-reset-hard, modus-themes-key-binding)
(modus-themes-search-success, modus-themes-search-success-modeline)
(modus-themes-search-success-lazy): Add new ':group' specification for
custom faces.

(modus-themes-operandi-color-overrides)
(modus-themes-vivendi-color-overrides, modus-themes-bold-constructs)
(modus-themes-variable-pitch-headings, modus-themes-variable-pitch-ui)
(modus-themes-no-mixed-fonts, modus-themes-fringes)
(modus-themes-scale-headings, modus-themes-scale-1, modus-themes-scale-2)
(modus-themes-scale-3, modus-themes-scale-4, modus-themes-scale-title)
(modus-themes-org-blocks, modus-themes-completions)
(modus-themes-success-deuteranopia, modus-themes-mail-citations)
(modus-themes-subtle-line-numbers, modus-themes-intense-hl-line): Add
custom setter.

(modus-themes-scale-5, modus-themes-scale-title): Deprecate variable
and replace it with alias 'modus-themes-scale-title'.

(modus-themes-slanted-constructs, modus-themes-italic-constructs):
Deprecate variable and replace it with alias
'modus-themes-italic-constructs'.

(modus-themes-org-habit, modus-themes-org-agenda): Deprecate variable
and make its functionality a part of 'modus-themes-org-agenda'.

(modus-themes-headings, modus-themes-mode-line, modus-themes-diffs)
(modus-themes-prompts, modus-themes-paren-match, modus-themes-syntax)
(modus-themes-links, modus-themes-region, modus-themes-lang-checkers)
(modus-themes-org-blocks): Make user options accept a value as a list
of properties.

(modus-themes--mixed-fonts, modus-themes--slant)
(modus-themes--fixed-pitch, modus-themes--lang-check)
(modus-themes--prompt, modus-themes--paren)
(modus-themes--syntax-foreground, modus-themes--syntax-extra)
(modus-themes--syntax-string, modus-themes--syntax-docstring)
(modus-themes--syntax-comment, modus-themes--heading-p)
(modus-themes--heading, modus-themes--org-habit)
(modus-themes--mode-line-attrs, modus-themes--link-color)
(modus-themes--link, modus-themes--region, modus-themes--hl-line):
Update internal functions to parse new values for user options.

* etc/themes/modus-operandi-theme.el,
  etc/themes/modus-vivendi-theme.el: Bump version number.

A detailed change log is provided here (no javascript required):
<https://protesilaos.com/codelog/2021-07-15-modus-themes-1-5-0/>.