holderadded event

[KitaitiMakoto]

@satorumurmur Hi,

I think it's helpful if we can know when BiB/i's holder span element is added to DOM tree so that we can find and manipulate it safely. This pull request is for that needs.

Of course, there are something to consider carefully like event name(holderadded), namespace(bibi:) and timing to dispatch. But, can you start with consideration whether BiB/i should have event API or not? I will rewrite patch if needed.

Thanks.

[KitaitiMakoto]

I'd appreciate if @shunito comments on this topic from the perspective of the plugin system developer.

[satorumurmur]

Thanks.

The embedder script "bib/i.js" (it's called "Pipi" from me) does;

1. Search placeholder "a" elements with "data-bibi" and "href" attribute in HTML DOM.
2. Create and insert "span.bibi-holder" element before each placeholder "a".
3. Create and append "iframe.bibi-frame" element to each "span.bibi-holder", and load BiB/i.
4. (Make some UIs for entering fullscreen or opening another window and so on.)

By marging your request;

• Pipi let placeholder "a" dispatch a custom "bibi:holderadded" event.
• after "iframe.bibi-frame" had been appended to "span.bibi-holder".

It's very useful.

[KitaitiMakoto]

Thanks fir the details of Pipi and merging my paches.