Structured data for street addresses

[paulschreiber]

Resolves #21.

[jamesturk]

Moving comments over here from the issue:

The rationale could use a bit more work. This is maybe only the second or third request for this in many years, I think that more clear examples of where the current irregularities cause problems would be helpful. Especially as we discuss alternatives prior to accepting this.

For example, one other alternative we discussed was keeping the address field, but having formal delimiters. If the proposal is deciding against that I think it should be discussed in the rationale.

I'd add to Drawbacks:

• this complicates scrapers, which will now be responsible for splitting addresses in most cases.. a hard problem
  we could consider an alternative where this work is done post-scrape
• merging 7000+ addresses will be a big undertaking. Updating the scrapers alone doesn't handle that.
• currently all fields are atomic, which makes merging/linting easier, but now we need to be sure to treat these new fields as a unit

And one small copy/paste typo in implementation plan, "committee scrapers".