Implement the openaddresses import module.

lib/addresses/openaddresses.js
  -Create a module for importing openaddresses.
  -Define `filter()`, `normalizer()`, and `addressStream()`.
Add unit test module for openaddresses.

test/openaddresses.js
  -Add a unit-test module for `lib/addresses/openaddresses`.
  -Define a test for `filter()`.
Add unit-test for openaddresses.normalizer().

test/openaddresses.js
  -Add a unit-test for `normalizer()`.
Add openaddresses to import entry point.

index.js
  -Add a flag to import openaddresses to the import script.

index.js, package.json
    -Refactor `lib/address` module `require`ing using the
    `require-dir` module.
Merge branch 'feature/openaddresses' into develop

index.js, lib/addresses/openaddresses.js
  -Add a module to import OpenAddresses.
  -Integrate it in the import script's main entry point.