Add HTML/DOM embed output options for PDFs in webapps

[MonsieurV]

When a PDF document is compiled from browser js clients with the POST/Json API, the return of /build/sync is not so obvious to exploit: as it is the PDF binary, the embedding of the PDF in the DOM/HTML is not trivial.

We should add output options for rendering embedding really easy in web application (without having to rely on the limited GET/querystring API).

Some ideas:

• create a compilation endpoint when we could get an URL for the generated PDF (so it can be used in embeds) (require the endpoint to be async in nature?)
• add an output mode which deliver a complete page with PDF.js, to be integrated in iframe (so the in-browser display of PDF is supported everywhere without requiring the users to host and handle themselves the PDF.js library)
• create a js/npm library wrapper with embedding functions