Update modus-themes to version 1.7.0

Update modus-themes to version 1.7.0

* doc/misc/modus-themes.org (File): Use new version and add release
date.
(How do the themes look like, Learn about the latest changes): Update
link to new URL.
(Enable and load): Update text of internal reference.
(Sample configuration for use-package): Add sample configuration
without the 'use-package' infrastructure.
(Differences between loading and enabling): Minor rewordings.
(Customization Options): Update sample code to cover latest changes.

(Option for inhibiting theme reload)
(Option for color-coding success state (deuteranopia))
(Option for more bold constructs)
(Option for more italic constructs)
(Option for syntax highlighting)
(Option for links)
(Option for command prompt styles)
(Option for mode line presentation)
(Option for accented background in tab interfaces)
(Option for completion framework aesthetics)
(Option for mail citations)
(Option for fringe visibility)
(Option for language checkers)
(Option for line highlighting (hl-line-mode))
(Option for line numbers (display-line-numbers-mode))
(Option for parenthesis matching (show-paren-mode))
(Option for active region)
(Option for diff buffer looks)
(Option for org-mode block styles)
(Option for Org agenda constructs)
(Option for scaled headings)
(Control the scale of headings)
(Option for variable-pitch font in UI elements)
(Option for variable-pitch font in headings): Write brief description,
document the type of the user option, and make any other relevant
adjustments.

(Option for font mixing): Document new 'modus-themes-mixed-fonts' user
option, which supersedes the old 'modus-themes-no-mixed-fonts'.
(Option for mode line padding): Document new user option
'modus-themes-mode-line-padding'.
(Option for language checkers): Include new available property for the
user option 'modus-themes-lang-checkers'.  Reword the rest of the
entry.
(Option for intense markup in Org and others): Describe new boolean
option 'modus-themes-intense-markup'.
(Option for Org agenda constructs): Include new available property for
the 'event' key in the alist 'modus-themes-org-agenda'.
(Option for the headings' overall style): Describe the new style of
explicitly specifying an optional font weight other than the implied
bold.

(Font configurations for Org and others (DIY))
(Configure bold and italic faces (DIY)): Reword and clarify some
statements.
(Decrease mode line height (DIY)): Add new Do-It-Yourself section on
tweaking the mode line's :box attribute.
(Full support for packages or face groups): Include new packages.
(Acknowledgements): Update list of contributors to code, user
feedback, etc.  Does not affect the status of copyright assignment.
(Meta): Update URLs to protesilaos.com (my website).

* etc/themes/modus-themes.el (modus-themes-variable-pitch)
(modus-themes-fixed-pitch, modus-themes-no-mixed-fonts): Reference the
new 'modus-themes-mixed-fonts' user option.
(modus-themes--headings-choice): Include new font weight styles.
(modus-themes-headings): Document the new feature of accepting an
explicit font weight.
(modus-themes-org-agenda): Document the refinements to the 'event' key
of the alist and the new 'varied' property it accepts.
(modus-themes-lang-checkers): Describe the new 'faint' property.
(modus-themes-mode-line-padding): Include new user option.
(modus-themes-intense-hl-line): Remove old-deprecated user option.
(modus-themes-intense-markup): Add new option.
(modus-themes-success-deuteranopia): Update doc string.
(modus-themes--fixed-pitch): Work with 'modus-themes-mixed-fonts'.
(modus-themes--lang-check): Update internal function to add the
'faint' property of 'modus-themes-lang-checkers'.
(modus-themes--markup): Add helper function.
(modus-themes--heading-weights): Private variable with available font
weights.
(modus-themes--heading-weight): New helper function to pick the
desired font weight.
(modus-themes--heading): Update helper function to implement the
aforementioned change to 'modus-themes-headings'.
(modus-themes--agenda-event): Update helper function to apply the new
styles of 'modus-themes-org-agenda'.
(modus-themes--mode-line-padding): Add helper function for
'modus-themes-mode-line-padding'.
(modus-themes--mode-line-attrs): Minor refinements.
(modus-themes-load-operandi, modus-themes-load-vivendi): Make these
functions interactive.
(modus-themes-faces): Update faces.

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

* * *

A detailed change log entry is available here:
<https://protesilaos.com/codelog/2021-11-18-modus-themes-1-7-0/>.