ICU-12865 Update API docs to reflect new features in ICU 54 and later :-)

Author: pedberg-icu

icu4c/source/i18n/unicode/reldatefmt.h

@@ -384,8 +384,10 @@ class U_I18N_API FormattedRelativeDateTime : public UMemory, public FormattedVal
  * </pre>
  * </blockquote>
  * <p>
- * In the future, we may add more forms, such as abbreviated/short forms
- * (3 secs ago), and relative day periods ("yesterday afternoon"), etc.
+ * The UDateRelativeDateTimeFormatterStyle parameter allows selection of
+ * different length styles: LONG ("3 seconds ago"), SHORT ("3 sec. ago"),
+ * NARROW ("3s ago"). In the future, we may add more forms, such as
+ * relative day periods ("yesterday afternoon"), etc.
  *
  * The RelativeDateTimeFormatter class is not intended for public subclassing.
  *

icu4j/main/core/src/main/java/com/ibm/icu/text/RelativeDateTimeFormatter.java

@@ -73,8 +73,10 @@
  * </pre>
  * </blockquote>
  * <p>
- * In the future, we may add more forms, such as abbreviated/short forms
- * (3 secs ago), and relative day periods ("yesterday afternoon"), etc.
+ * The Style parameter allows selection of different length styles:
+ * LONG ("3 seconds ago"), SHORT ("3 sec. ago"), NARROW ("3s ago").
+ * In the future, we may add more forms, such as relative day periods
+ * ("yesterday afternoon"), etc.
  *
  * @stable ICU 53
  */