Revise C++ coding style using clang-format-6.0

Run the `clang-format.bash` script to update all our C and C++ code to a
new style defined by `.clang-format`.  Use `clang-format` version 6.0.

* If you reached this commit for a line in `git blame`, re-run the blame
  operation starting at the parent of this commit to see older history
  for the content.

* See the parent commit for instructions to rebase a change across this
  style transition commit.

Tests/Tutorial/Step2/tutorial.cxx

@@ -5,7 +5,7 @@
 #include <stdlib.h>
 
 #ifdef USE_MYMATH
-#include "MathFunctions.h"
+#  include "MathFunctions.h"
 #endif
 
 int main(int argc, char* argv[])