Update doxygen for cffi docs (#4136)

fix styling

deltachat-ffi/Doxyfile.css

@@ -1,14 +1,24 @@
 
+:root {
+	--accent: hsl(0 0% 70%);
+}
+
+@media (prefers-color-scheme: dark) {
+	:root {
+		--accent: hsl(0 0% 30%);
+	}
+}
+
 /* the code snippet frame, defaults to white which tends to get badly readable in combination with explaining text around */
 div.fragment {
-	background-color: #e0e0e0;
+	background-color: var(--accent);
 	border: 0;
 	padding: 1em;
 	border-radius: 6px;
 }
 
 code {
-	background-color: #e0e0e0;
+	background-color: var(--accent);
 	padding-left: .5em;
 	padding-right: .5em;
 	border-radius: 6px;

deltachat-ffi/deltachat.h

@@ -6623,7 +6623,7 @@ void dc_event_unref(dc_event_t* event);
 
 /// "You changed your email address from %1$s to %2$s.
 /// If you now send a message to a group, contacts there will automatically
-/// replace the old with your new address.\n\nIt's highly advised to set up 
+/// replace the old with your new address.\n\n It's highly advised to set up 
 /// your old email provider to forward all emails to your new email address. 
 /// Otherwise you might miss messages of contacts who did not get your new 
 /// address yet." + the link to the AEAP blog post