Basic destination sign handling.

This first part in our Exit Sign / Destination Sign quest re-wires
the `destination=` and `destination:ref=` tag to the `ref=` tag (in case
it's the highway does not already have a `ref=` tag).

Doing some analysis on both Berlin and San Francisco it looks like this
will add a couple of thousand `ref=` tags that we will announce in guidance.

References:
- https://github.com/Project-OSRM/osrm-backend/issues/2267#issuecomment-214771682
- http://wiki.openstreetmap.org/wiki/Key:destination
- http://wiki.openstreetmap.org/wiki/Proposed_features/Destination_details

features/guidance/destination-signs.feature

@@ -0,0 +1,33 @@
+@routing @guidance
+Feature: Destination Signs
+
+    Background:
+        Given the profile "car"
+
+    Scenario: Car - route name assembly with destination signs
+        Given the node map
+          | a | b |
+          | c | d |
+          | e | f |
+          | g | h |
+          | i | j |
+          | k | l |
+          | m | n |
+
+        And the ways
+          | nodes | name | ref | destination | destination:ref |
+          | ab    | AB   | E1  |             |                 |
+          | cd    | CD   |     | Berlin      |                 |
+          | ef    | EF   |     | Berlin      | A1              |
+          | gh    |      |     | Berlin      | A1              |
+          | ij    |      |     | Berlin      |                 |
+          | kl    | KL   | E1  | Berlin      | A1              |
+
+        When I route I should get
+          | from | to | route                           |
+          | a    | b  | AB (E1),AB (E1)                 |
+          | c    | d  | CD (Berlin),CD (Berlin)         |
+          | e    | f  | EF (A1: Berlin),EF (A1: Berlin) |
+          | g    | h  | ,                               |
+          | i    | j  | ,                               |
+          | k    | l  | KL (E1),KL (E1)                 |

profiles/car.lua

@@ -1,6 +1,7 @@
 -- Car profile
 
 local find_access_tag = require("lib/access").find_access_tag
+local get_destination = require("lib/destination").get_destination
 
 -- Begin of globals
 barrier_whitelist = { ["cattle_grid"] = true, ["border_control"] = true, ["checkpoint"] = true, ["toll_booth"] = true, ["sally_port"] = true, ["gate"] = true, ["lift_gate"] = true, ["no"] = true, ["entrance"] = true }
@@ -352,15 +353,19 @@ function way_function (way, result)
   -- local barrier = way:get_value_by_key("barrier", "")
   -- local cycleway = way:get_value_by_key("cycleway", "")
   local service = way:get_value_by_key("service")
+  local destination = get_destination(way)
 
   -- Set the name that will be used for instructions
   local has_ref = ref and "" ~= ref
   local has_name = name and "" ~= name
+  local has_destination = destination and "" ~= destination
 
   if has_name and has_ref then
     result.name = name .. " (" .. ref .. ")"
   elseif has_ref then
     result.name = ref
+  elseif has_name and has_destination then
+    result.name = name .. " (" .. destination .. ")"
   elseif has_name then
     result.name = name
 --  else

profiles/lib/destination.lua

@@ -0,0 +1,27 @@
+local Destination = {}
+
+function Destination.get_destination(way)
+  local destination = way:get_value_by_key("destination")
+  local destination_ref = way:get_value_by_key("destination:ref")
+
+  -- Assemble destination as: "A59: Düsseldorf, Köln"
+  --          destination:ref  ^    ^  destination
+
+  local rv = ""
+
+  if destination_ref and destination_ref ~= "" then
+    rv = rv .. destination_ref
+  end
+
+  if destination and destination ~= "" then
+      if rv ~= "" then
+          rv = rv .. ": "
+      end
+
+      rv = rv .. string.gsub(destination, ";", ", ")
+  end
+
+  return rv
+end
+
+return Destination

taginfo.json

@@ -204,6 +204,16 @@
             "object_types": [ "way" ],
             "description": "Ref of road for navigation instructions, overrides name."
         },
+        {
+            "key": "destination",
+            "object_types": [ "way" ],
+            "description": "Destination of road for navigation instructions, supplements name."
+        },
+        {
+            "key": "destination:ref",
+            "object_types": [ "way" ],
+            "description": "Destination of road for navigation instructions, supplements name."
+        },
         {
             "key": "junction",
             "object_types": [ "way" ],