Allowing moment.set() to accept a hash of units

[jordaaash]

Setting multiple values using the chaining API is awkward and verbose.

Currently:

moment().set('year', 2011).set('month', 9).set('date', 12).set('hours', 6).set('minutes', 7).set('seconds', 8);

After this patch, the current API is supported, as well as using a hash of values:

moment().set({ year: 2011, month: 9, date: 12, hours: 6, minutes: 7, seconds: 8 });

PR includes a passing test for the new behavior.

[ichernev]

I think we need to enforce an order for setting the properties: from bigger units to smaller.

Also we need a few more tests that cover passing {} and null.

[jordaaash]

Got it. I'm not very familiar with moment's internals. What's the purpose of the ordering?
Also, I'm guessing it should noop on {} and return this. Should it also noop on null, should it error, or should it do something else (like a "clear" function)?

[ichernev]

Nooping is fine. Ordering is for more consistent and less surprising results.

[ichernev]

Merged in 81a3b7b