Allow optionsValue to accept an array map

[nathanboktae]

My initial instinct on using optionsValue was to pass it an array that was a map of the values in the options box, but I was surprised that it wasn't supported. This is very common for things that need to be localized.

[mbest]

Since optionsValue can be a function, it's easy enough to make it do what you want. Maybe we could add the index as a second parameter to the function since it looks like you want to use the index as input.

[nathanboktae]

It is easy enough to use a function, but to keep views logicless as possible and view models as simple as possible, it's nice to have. I bring up localization as it can be such a cross cutting concern and not something you would want to put on every view model.

var l10n = {
  'ko-KR': {
    cat: '고양이',
    dog: '개',
    bird: '새'
  }
};
var model = {
  pets: ['cat', 'dog', 'bird'];
};

<select data-bind="options: pets, optionsText: l10n['ko-KR']"></select>

Though with the first commit, I didn't have that situation flushed out :) For such a low-impact, trivial work it seems nice to flush out the usage of this binding a bit more.