WIP: Use Libpostal service

[orangejulius]

Looking for early review, not 100% production ready yet

Use microservice-wrapper to avoid having to load libpostal locally.

~Note: this now requires a new configuration section in pelias.json, a top-level services key with the usual properties. Here's an example full pelias.json:~

Update: The code will fall back to api.services.libpostal if services.libpostal is not defined. This helps ensure backwards compatibility.

{
  "api": {
    "textAnalyzer": "libpostal"
  },
  "services": {
    "libpostal": {
      "url": "http://libpostal-service-url:8080",
      "timeout": 4000
    }
  }
}

Notes

This is a breaking change, since a new configuration option is required.

~The deasync module was chosen to give the libpostal service a synchronous-like interface. We should carefully evaluate whether there are any issues with this. We can avoid using it, however it would be quite a bit of work, as many sections of the code, including lots of unit tests, would have to be re-written in a callback style.~

See update below, this code has now been rewritten in an asynchronous style.

Fixes: https://github.com/pelias/interpolation/issues/106

[orangejulius]

This has now been rewritten to use Promises, async/await, and asynchronous interfaces in general. It's a lot of changed code, and I'm actually not an expert in using the new asynchronous tools in newer Javascript in production. In practice I think we'll need more try/catch blocks or general error handling for asynchronous code failures. I think even something like a single intermittent network glitch could crash the service right now.

However this should be a big change as the interpolation service will take only a few MB of RAM, and is thus much easier and cheaper to deploy.

[orangejulius]

Turns out there is some more work to do:

• We will probably want to add some logging of structured data regarding each request to libpostal, including the query that was sent and how long it took to get a response
• In to record response time information, pelias-microservice-wrapper exposes a metadata object as a 3rd parameter returned to callback functions. This makes it a bit harder to use util.promisify, so sticking with a standard callback architecture where possible might be best
• Finally, while doing some more testing of the interpolation service it turns out that the demo is broken because the /extract/geojson endpoint was not converted to use the libpostal service. It's a challenging endpoint that needs to normalize multiple street names and therefore can generate multiple calls to the libpostal service, so this will take some work.