Add support for multiple Gravatar services

Now supports Libravatar and Unicornify, next to Gravatar (Bug#39965).

* lisp/image/gravatar.el (gravatar-base-url): Remove constant.
(gravatar-service-alist): List supported services.
(gravatar-service): Add user option to specify service, defaults to
Libravatar.
(gravatar--service-libravatar): New function, libravatar image host
resolver implementation.
(gravatar-build-url): Use alist gravatar-service-alist instead of
gravatar-base-url.
* etc/NEWS: Mention new gravatar service option.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index ba3e691ff91..2150f49b432 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -186,6 +186,12 @@ key             binding
 / v             package-menu-filter-by-version
 / /             package-menu-filter-clear
 
+** Gravatar
+
+===
+*** New user option 'gravatar-service' for host to query for gravatars.
+Defaults to Libravatar, with Unicornify and Gravatar as options.
+
 
 * New Modes and Packages in Emacs 28.1