PERF: Replace explicit return calls of constructor

Replaces explicit calls to the constructor in a return with a braced
initializer list. This way the return type is not needlessly duplicated in the
function definition and the return statement.

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-return-braced-init-list  -header-filter=.* -fix

src/lib_json/json_reader.cpp

@@ -69,7 +69,7 @@ Features::Features()
     : allowComments_(true), strictRoot_(false),
       allowDroppedNullPlaceholders_(false), allowNumericKeys_(false) {}
 
-Features Features::all() { return Features(); }
+Features Features::all() { return {}; }
 
 Features Features::strictMode() {
   Features features;
@@ -906,7 +906,7 @@ public:
 // exact copy of Implementation of class Features
 // ////////////////////////////////
 
-OurFeatures OurFeatures::all() { return OurFeatures(); }
+OurFeatures OurFeatures::all() { return {}; }
 
 // Implementation of class Reader
 // ////////////////////////////////

src/lib_json/json_value.cpp

@@ -1507,7 +1507,7 @@ Value::const_iterator Value::begin() const {
   default:
     break;
   }
-  return const_iterator();
+  return {};
 }
 
 Value::const_iterator Value::end() const {
@@ -1520,7 +1520,7 @@ Value::const_iterator Value::end() const {
   default:
     break;
   }
-  return const_iterator();
+  return {};
 }
 
 Value::iterator Value::begin() {