`try ... catch` syntax

The following discussion from !63 (merged) should be addressed:

• @paconnor started a discussion:

  I have changed the template in CONTRIBUTING.md with the following syntax:

  int main (int argc, char * argv[])
  try {
      // blah
      return EXIT_SUCCESS;
  }
  catch (boost::exception& e) {
      DE::Diagnostic(e); // this function belongs to `Darwin::Exceptions`
      return EXIT_FAILURE;
  }

  to reduce the indentation. I also find it more readable. Do we want to apply this change everywhere else?