Add expressway tagging to the transportation layer (#1313)

Fixes #1148 

This PR adds expressway tagging to the `transportation` layer, by setting `expressway=1` for non-motorway roads tagged `expressway=yes`, and omitting the tag otherwise.  Additionally, I've added a few unit tests to verify that the expressway tagging is being imported and updated into the intermediate tables.

Here is an example of expressway tagging on US-1 in Rhode Island, USA:

![image](https://user-images.githubusercontent.com/3254090/143501278-db3671b2-2efa-4998-bffd-9ddfec63579b.png)

layers/transportation/transportation.yaml

@@ -162,6 +162,10 @@ layer:
       description: |
           Whether this is a toll road, based on the [`toll`](http://wiki.openstreetmap.org/wiki/Key:toll) tag.
       values: [0, 1]
+    expressway:
+      description: |
+          Whether this is an expressway, based on the [`expressway`](http://wiki.openstreetmap.org/wiki/Key:expressway) tag.
+      values: [1]
     layer:
       description: |
           Original value of the [`layer`](http://wiki.openstreetmap.org/wiki/Key:layer) tag.
@@ -196,7 +200,7 @@ layer:
   datasource:
     geometry_field: geometry
     srid: 900913
-    query: (SELECT geometry, class, subclass, network, oneway, ramp, brunnel, service, access, toll, layer, level, indoor, bicycle, foot, horse, mtb_scale, surface FROM layer_transportation(!bbox!, z(!scale_denominator!))) AS t
+    query: (SELECT geometry, class, subclass, network, oneway, ramp, brunnel, service, access, toll, expressway, layer, level, indoor, bicycle, foot, horse, mtb_scale, surface FROM layer_transportation(!bbox!, z(!scale_denominator!))) AS t
 schema:
   - ./network_type.sql
   - ./class.sql