Consider adding spec authors

[tidoust]

Many entries in Specref list the authors of the specification. We do not collect this information in browser-specs, because I don't think anyone asked for the information so far. That said, this becomes needed for browser-specs to provide more entries to Specref.

For example, browser-specs contains all WHATWG specs, but cannot replace the WHATWG source in Specref right away because it does not list spec authors.

Some considerations:

• The list of authors can easily be retrieved from the W3C API, from the WHATWG spec database, and from the JSON document that describes an IETF spec.
• The list of authors can easily be extracted from a W3C spec as well.
• Beyond that, extraction may need to be more ad-hoc.
• There is a recurring discussion about distinguishing between authors and editors. Specs typically do not make that distinction, so I'm not sure we can do any better than having a raw list of names.