Add basic facades for Extractor and Contractor run methods.

Based on idea suggested in comments to #3776, simplifies
use of extractor and contractor as libraries.

src/osrm/contractor.cpp

@@ -0,0 +1,12 @@
+#include "osrm/contractor.hpp"
+#include "contractor/contractor.hpp"
+#include "contractor/contractor_config.hpp"
+
+namespace osrm
+{
+
+// Pimpl-like facade
+
+void contract(const contractor::ContractorConfig &config) { contractor::Contractor(config).Run(); }
+
+} // ns osrm

src/osrm/extractor.cpp

@@ -0,0 +1,17 @@
+#include "osrm/extractor.hpp"
+#include "extractor/extractor.hpp"
+#include "extractor/extractor_config.hpp"
+#include "extractor/scripting_environment_lua.hpp"
+
+namespace osrm
+{
+
+// Pimpl-like facade
+
+void extract(const extractor::ExtractorConfig &config)
+{
+    extractor::Sol2ScriptingEnvironment scripting_environment(config.profile_path.string().c_str());
+    extractor::Extractor(config).run(scripting_environment);
+}
+
+} // ns osrm