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

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