v21

• Tracing now includes return values and exceptions thrown.
  For exception types inherited from std::exception, the
  what() string is printed.
• Fixed a bug when a member function in a mocked class calls
  a mocked function. This is now explicitly allowed, even
  when an expectation recursively calls the same function
  as a side effect.
• Worked around VisualStudio 2015 update 3 issue where trailing
  return type for lambdas is not respected in template deduction
  context. This caused compilation errors when using matchers
  in expectations to overloaded functions.
• Worked around VisualStudio 2015 update 3 issue with evaluating
  regex_search() in trailing return type spec for auto deduced
  string type.