Syntax decision

[Zhong Yu]

Since 0-arg case is quite common, as in Runnable and Callable, we'll
have many use cases like

    cache.get(key, ()->load(key));

    tasks.add(()->{ doSomething(arg);});

    transaction(()->{
        statement1;
        statement2;
    });

Not bad after staring at them for 30 minutes. But too many consecutive
punctuation marks are there... quite dizzy at first sight.

How about a single punctuation mark, currently unused, as syntax sugar
for "()->". Too cheesy?

- Zhong Yu