Set avatars and custom emoji as square (fixes display in Dillo)

The minimalist web browser Dillo has recently started up development
again. Its CSS implementation only applies the explicitly stated
width and height of an image, so avatars were displaying at 2.5 em high,
and the full original width.
https://dillo-browser.github.io/

html.c

@@ -55,7 +55,7 @@ xs_str *replace_shortnames(xs_str *s, xs_list *tag, int ems)
             tag_list = xs_dup(tag);
         }
 
-        xs *style = xs_fmt("height: %dem; vertical-align: middle;", ems);
+        xs *style = xs_fmt("height: %dem; width: %dem; vertical-align: middle;", ems, ems);
 
         xs_list *p = tag_list;
         char *v;

utils.c

@@ -49,7 +49,7 @@ static const char *default_css =
     ".snac-top-user { text-align: center; padding-bottom: 2em }\n"
     ".snac-top-user-name { font-size: 200% }\n"
     ".snac-top-user-id { font-size: 150% }\n"
-    ".snac-avatar { float: left; height: 2.5em; padding: 0.25em }\n"
+    ".snac-avatar { float: left; height: 2.5em; width: 2.5em; padding: 0.25em }\n"
     ".snac-author { font-size: 90%; text-decoration: none }\n"
     ".snac-author-tag { font-size: 80% }\n"
     ".snac-pubdate { color: #a0a0a0; font-size: 90% }\n"