Implement raster source feature to read data from third-party sources, to be used in lua profiles.

* Adds a data structure, RasterSource, to store parsed + queryable data
* Adds bindings for that and relevant data structures as well as source_function and segment_function
* Adds relevant unit tests and cucumber tests
* Bring-your-own-data feature

features/raster/extract.feature

@@ -0,0 +1,18 @@
+@raster @extract
+Feature: osrm-extract with a profile containing raster source
+# expansions:
+# {osm_base} => path to current input file
+# {profile} => path to current profile script
+
+    Scenario: osrm-extract on a valid profile
+        Given the profile "rasterbot"
+        And the node map
+            | a | b |
+        And the ways
+            | nodes |
+            | ab    |
+        And the data has been saved to disk
+        When I run "osrm-extract {osm_base}.osm -p {profile}"
+        Then stderr should be empty
+        And stdout should contain "source loader"
+        And it should exit with code 0