Merge branch 'feature/rename_address_props' into develop

lib/address.js
	-Rename most `Address` properties to conform to the schema
	required by the address-deduplicator
	(https://github.com/openvenues/address_normalizer/blob/master/
		address_normalizer/models/address.py).
Add a deduplicate stream module.

lib/deduplicate_stream.js
	-Add a module that exposes a stream to deduplicate addresses
	coming down the pipeline.
	-Currently a little rough around the edges: undocumented,
	lightly tested, etc.
Refactor the deduplicate_stream module.

lib/deduplicate_stream.js
	-Restructure the `deduplicate_stream` module, abstracting chunks
	of functionality into functions (eg, `sendBatch()`,
	`bufferBatch()`).
Thoroughly document the duplicates_stream module.

lib/deduplicate_stream.js
	-Add documentation to the module header, all functions, and
	tricky code.
Convert from through to through2.

lib/(addresses/(openaddresses, osm, tiger), dataset_import).js
	-Convert from the `through` module to the more up-to-date
	`through2`, which uses the streams2 API.
Rate limit deduplicate_stream.

lib/deduplicate_stream.js
	-Implement rate-limiting in the stream exported by the
	`deduplicate_stream` module, to prevent it from throttling the
	slower deduper.
Document the deduplicate_stream's rate-limiting.

lib/deduplicate_stream.js
	-Add an argument `maxLiveRequests` to
	`createDeduplicateStream()`, which allows the caller to
	configure the stream's rate-limiting.
	-Add documentation regarding rate-limiting.
Update package.json dependencies.

package.json
	-Add the dependencies required by the features added in this
	branch.
Merge branch 'feature/deduplicate' into develop

lib/deduplicate_stream.js
	-Add a module that interfaces with the pipeline's external
	address deduper to deduplicate a stream of addresses.