Replace testImports() with handleUserArgs().

index.js
  -Replace `testImports()` with a `handleUserArgs()`, which will
  cater data imports directly to user arguments.
Complete handleUserArgs().

index.js
  -Define `createFileAddressStreams()`, for use in `handleUserArgs()`.
  -Create combined address streams for specified OSM/TIGER data.
Add documentation comments to index.js.

index.js
  -Add documentation comments to `handleUserArgs()`,
  `createFileAddressStreams()`, and the module header.
Merge branch 'feature/user_input' into develop

index.js
  -Add support for command-line user arguments.