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

include/json/reader.h

@@ -256,7 +256,7 @@ private:
  */
 class JSON_API CharReader {
 public:
-  virtual ~CharReader() {}
+  virtual ~CharReader() = default;
   /** \brief Read a Value from a <a HREF="http://www.json.org">JSON</a>
    document.
    * The document must be a UTF-8 encoded string containing the document to
@@ -282,7 +282,7 @@ public:
 
   class JSON_API Factory {
   public:
-    virtual ~Factory() {}
+    virtual ~Factory() = default;
     /** \brief Allocate a CharReader via operator new().
      * \throw std::exception if something goes wrong (e.g. invalid settings)
      */