issue #2790: Updates comments for Map<K, V> container.

Signed-off-by: James Chen <jianhua.chen@cocos2d-x.org>
issue #2790: Comment fix for Map<K, V>::clear.

Signed-off-by: James Chen <jianhua.chen@cocos2d-x.org>
issue #2790: Adds comments for Vector<T>.

Signed-off-by: James Chen <jianhua.chen@cocos2d-x.org>
Merge pull request #4476 from dumganhar/iss2790-container-comments

issue #2790: Updates comments for Map<K, V> and Vector<T> container.