Move to asynchronous input parsing

[larsgw]

Parsing input sometimes requires calls to e.g. the Wikidata API, but with the current setup, this has to use synchronous requests, something that should be avoided. I propose the following syntax:

Cite.parseInput(<data>, <optional: callback>)

function callback (result) {
  result // Parsed input (CSL-JSON)
}

Not providing callback (when required) will cause a warning and will probably be deprecated in the next version (so either v0.4 or v1.0). I could add both parseInput and parseInputAsync, to avoid the optional callback and just warning/throwing an error when parseInput is used when requests need to be made.

The following is possible too (perhaps both?):

Cite(<data>, <optional: options>, <optional: callback>)

function callback (result) {
  result // Cite object
}

This, however, has at least all the problems the one above has, and probably more.