Fix OSM unit tests.

test/(address-normalizer -> osm).js
  -The `osm` import module initially existed as
  `address-normalization` in the project root.
  -Rename the corresponding test module, and update its `require()`
  path accordingly.. since the module wasn't changed, all tests are
  functional and passing.

lib/addresses/osm.js
  -Export `filter()` and `normalizer()` as well to facilitate testing.