STYLE: Pefer = default to explicitly trivial implementations

This check replaces default bodies of special member functions with
= default;. The explicitly defaulted function declarations enable more
opportunities in optimization, because the compiler might treat
explicitly defaulted functions as trivial.

Additionally, the C++11 use of = default more clearly expreses the
intent for the special member functions.

SRCDIR=/Users/johnsonhj/src/jsoncpp/ #My local SRC
BLDDIR=/Users/johnsonhj/src/jsoncpp/cmake-build-debug/ #My local BLD

cd /Users/johnsonhj/src/jsoncpp/cmake-build-debug/
run-clang-tidy.py -extra-arg=-D__clang__ -checks=-*,modernize-use-equals-default  -header-filter=.* -fix

src/lib_json/json_reader.cpp

@@ -60,7 +60,7 @@ typedef std::auto_ptr<CharReader> CharReaderPtr;
 // ////////////////////////////////
 
 Features::Features()
-     {}
+     = default;
 
 Features Features::all() { return {}; }
 
@@ -1907,7 +1907,7 @@ public:
 };
 
 CharReaderBuilder::CharReaderBuilder() { setDefaults(&settings_); }
-CharReaderBuilder::~CharReaderBuilder() {}
+CharReaderBuilder::~CharReaderBuilder() = default;
 CharReader* CharReaderBuilder::newCharReader() const {
   bool collectComments = settings_["collectComments"].asBool();
   OurFeatures features = OurFeatures::all();