Make gravatar.el more configurable

For discussion, see the following thread:
https://lists.gnu.org/archive/html/emacs-devel/2019-07/msg00528.html

* etc/NEWS: Announce changes in gravatar.el user options.

* lisp/image/gravatar.el (gravatar-cache-ttl): Change :type to
number of seconds without changing the default value and while still
accepting other timestamp formats.
(gravatar-rating): Restrict :type to ratings recognized by Gravatar.
(gravatar-size): Allow nil as a value, in which case Gravatar's
default size is used.
(gravatar-default-image, gravatar-force-default): New user options
controlling the Gravatar query parameters 'default' and
'forcedefault', respectively.
(gravatar-base-url): Use HTTPS.
(gravatar--query-string): New helper function to facilitate testing.
(gravatar-build-url): Use it.

* test/lisp/image/gravatar-tests.el (gravatar-size)
(gravatar-default-image, gravatar-force-default)
(gravatar-build-url): New tests.

1 files changed, 16 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 9be10b4e797..e84c0d3ec53 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1788,6 +1788,22 @@ particular when the end of the buffer is visible in the window.
 Use 'mouse-wheel-mode' instead.  Note that 'mouse-wheel-mode' is
 already enabled by default on most graphical displays.
 
+** Gravatar
+
++++
+*** 'gravatar-cache-ttl' is now a number of seconds.
+The previously used timestamp format of a list of integers is still
+supported, but is deprecated.  The default value has not changed.
+
++++
+*** 'gravatar-size' can now be nil.
+This results in the use of Gravatar's default size of 80 pixels.
+
++++
+*** The default fallback gravatar is now configurable.
+This is possible using the new user options 'gravatar-default-image'
+and 'gravatar-force-default'.
+
 
 * New Modes and Packages in Emacs 27.1