Introduce datepicker API (open, close, openYears, onSelectMonth, onOpen...)

[alcalyn]

Introduces methods to handle a datepicker instance.

Example to help to fill our birthdate:

var dp = TinyDatePicker(document.querySelector('.modal-txt'));

dp.onOpen(function () {
    if (dp.isEmpty()) {
        dp.openYears();
    }
});

dp.onSelectYear(function () {
    dp.openMonths();
});

Api methods:

// Handle datepicker
dp.isEmpty();
dp.open();
dp.close();
dp.updateDate(date);
dp.openYears();
dp.openMonths();

// Events
dp.onOpen(callback);
dp.onSelectYear(callback);
dp.onSelectMonth(callback);

[chrisdavies]

Hey, thanks! I like the idea of adding extensibility points like this. I'm going to flesh it out with tests before merging it.

[chrisdavies]

I ended up taking your changes and tweaking them a bit. I'm passing the event handlers in via opts instead of adding a light-weight eventing system to the date picker. An eventing system is something we may add later, but it probably needs a mechanism for add and remove, and possibly other more robust things that I don't want to think about at the moment!

I updated the docs. But here is how your previous example would work.

    TinyDatePicker(document.querySelector('.txt-top-right'), {
        onOpen: function(dp) {
          if (dp.value === '') {
            dp.openYears();
          }
        },

        onSelectYear: function (dp) {
          dp.openMonths();
        }
      });