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/mapping.yaml

@@ -159,6 +159,10 @@ surface_field: &surface
   key: surface
   name: surface
   type: string
+expressway_field: &expressway
+  key: expressway
+  name: expressway
+  type: bool
 
 tables:
 # etldoc: imposm3 -> osm_highway_linestring
@@ -206,6 +210,7 @@ tables:
     - *mtb_scale
     - *sac_scale
     - *surface
+    - *expressway
     mapping:
       highway:
       - motorway