List months and weekdays

Allows for:

```js
moment.months();
moment.shortMonths();
moment.weekdays();
moment.weekdaysShort();
moment.weekdaysMin();
```

And they work for languages for where the monthsShort string is a decided by a function:

```js
moment.monthsShort("-MMM-");
```

Fixes, for example, #1053.