CHANGELOG.md: Release v1.4.0
CHANGELOG.md: Update notes for unreleased version
layouts/partials/meta-terms.html: Trailing slash

Hard code a trailing slash in URLs for categories and tags to avoid
an HTTP 301 redirect at the very least, and an HTTP 404 at the very
worst (depending on web server configuration).

This is a workaround for a problem caused by our manual construction
of URLs using the categories and tags strings in post front matter.
Hugo's own taxonomy tooling always uses a trailing slash.

See: https://github.com/alanorth/hugo-theme-bootstrap4-blog/issues/128
Use Font Awesome SVGs via JavaScript

This is a bit of "one step forward, two steps back" in that we are
now using the much more lean SVG icons—and only the ones we are ac
tually using—instead of having to download the two ~70KiB web font
files, but it means we need to use JavaScript.

This approache was inspired by the work @xekon did in #127.

See: https://fontawesome.com/how-to-use/on-the-web/advanced/svg-javascript-core
See: https://github.com/alanorth/hugo-theme-bootstrap4-blog/pull/127
CHANGELOG.md: Add note about Font Awesome 5
Regenerate static assets
Update to Font Awesome 5

Nothing really new as far as how we're using Font Awesome, but it is
good to keep up with the times and the tooling. Users that have used
custom fonts in their content or layouts will need to update their
icon prefixes from "fa" to "fas" or "fab" depending on which font
their icon comes from.

See: https://fontawesome.com/how-to-use/on-the-web/setup/upgrading-from-version-4
Regenerate static assets
source/scss/font-awesome.scss: Remove Google+ icon
CHANGELOG.md: Add note about Google Plus
layouts: Remove a few more references to GooglePlus

The sharing icons were removed in 2019, but these remained.
.build.yml: Use Node.js v12
theme.toml: Increase minimum Hugo version to 0.55

I think the new subresource integrity (SRI) stuff requires this.

See: https://gohugo.io/hugo-pipes/fingerprint/
README.md: Update comment about Node.js version

I've been using version 10 for a year or so. Looking at the Node.js
LTS schedule I see that version 12 is the latest LTS release so I
guess I'll start using that locally at least.

See: https://nodejs.org/en/about/releases/
add summaryLength to example config, for faster learning and prototyping.
Regenerate static assets
source/scss/bootstrap.scss: Copy new version number

Otherwise it is very confusing because the generated style.css has
the wrong version number.
Run npm update

New minor versions of a few libraries.
layouts/_default/baseof.html: Fix comment about RTL

It's not just Arabic anymore now that I added Farsi strings!
package.json: Fix typo in build script

This builds the right-to-left version of the stylesheet (RTL).