Add toll tagging (#1177)

Fixes #366

This PR sets `toll=1` in the `transportation` layer when a road is tagged as a toll road in OSM (with the tag `toll=yes`).  If a road is tagged with any other value of `tag=*`, the value is suppressed in the tile, since non-toll roads can be presumed as the default and therefore this PR should have only negligible impact in the tiles.

Support for toll road tagging is of interest in the American mapping community, because toll roads have historically been styled differently on American-style maps, for example:
![image](https://user-images.githubusercontent.com/3254090/129505967-5916eace-596a-4c89-ac5d-0aab3e641ed7.png)


Screen shot of a toll road being generated in the `transportation` layer tiles:
![image](https://user-images.githubusercontent.com/3254090/129505683-eb315643-95ff-455b-a606-f379f776f92d.png)

layers/transportation/mapping.yaml

@@ -96,6 +96,10 @@ access_field: &access
   key: access
   name: access
   type: string
+toll_field: &toll
+  key: toll
+  name: toll
+  type: bool
 usage_field: &usage
   key: usage
   name: usage
@@ -188,6 +192,7 @@ tables:
     - *area
     - *service
     - *access
+    - *toll
     - *usage
     - *public_transport
     - *man_made