Run clang-format on the public headers.
Also update copyright year.

Change-Id: I8508d4fd4564c646ec2281a1b3b2c36136b54b46
diff --git a/include/ceres/context.h b/include/ceres/context.h
index cf7c436..d08e32b 100644
--- a/include/ceres/context.h
+++ b/include/ceres/context.h
@@ -1,5 +1,5 @@
 // Ceres Solver - A fast non-linear least squares minimizer
-// Copyright 2018 Google Inc. All rights reserved.
+// Copyright 2019 Google Inc. All rights reserved.
 // http://ceres-solver.org/
 //
 // Redistribution and use in source and binary forms, with or without