Problem::Evaluate implementation.

1. Add Problem::Evaluate and tests.
2. Remove Solver::Summary::initial/final_*
3. Remove Solver::Options::return_* members.
4. Various cpplint cleanups.

Change-Id: I4266de53489896f72d9c6798c5efde6748d68a47
diff --git a/internal/ceres/wall_time.h b/internal/ceres/wall_time.h
index 1dbd6e9..45f65ca 100644
--- a/internal/ceres/wall_time.h
+++ b/internal/ceres/wall_time.h
@@ -72,7 +72,7 @@
 //     Total:  time3  time1 + time2 + time3;
 class EventLogger {
  public:
-  EventLogger(const string& logger_name);
+  explicit EventLogger(const string& logger_name);
   ~EventLogger();
   void AddEvent(const string& event_name);