Add doc and examples.

libraries/dateformatter/api/src/main/kotlin/io/element/android/libraries/dateformatter/api/DateFormatter.kt

@@ -16,11 +16,41 @@ interface DateFormatter {
 }
 
 enum class DateFormatterMode {
+    /**
+     * Full date and time.
+     * Example:
+     * "April 6, 1980 at 6:35 PM"
+     * Format can be shorter when useRelative is true.
+     * Example:
+     * "6:35 PM"
+     */
     Full,
+
+    /**
+     * Only month and year.
+     * Example:
+     * "April 1980"
+     * "This month" can be returned when useRelative is true.
+     * Example:
+     * "This month"
+     */
     Month,
+
+    /**
+     * Only day.
+     * Example:
+     * "Sunday 6 April"
+     * "Today", "Yesterday" and day of week can be returned when useRelative is true.
+     */
     Day,
-    // Time if same day, else date
+
+    /**
+     * Time if same day, else date.
+     */
     TimeOrDate,
-    // Only time whatever the day
+
+    /**
+     * Only time whatever the day.
+     */
     TimeOnly,
 }