Redefine addresses() to output a Readable stream.

lib/addresses/osm.js
  -Rename `addresses()` to `addressStream()`.
  -Redefine it to return its normalized/filtered Stream.
  -Add documentation comment.
Move Address() to own module, for reusability.

lib/(address, addresses/osm).js
  -Move the `Address()` constructor from `osm.js` to its own
  module, `address.js`, for reusability in other address modules.