add support for ISO 639-1 in Languages API

[guangrei]

hi, in some environment like web browser only support ISO 639-1, so its useful to add ISO 639-1 support, for example:

{
    "name": "French",
    "code": "fra",
    "alias": "fr"
  },

and we can use navigator.language.split('-')[0]; without 3rd library to convert into ISO 639-3

[freearhey]

the fact is that only a small fraction of languages have an ISO 639-1 code: https://en.wikipedia.org/wiki/ISO_639:a