PERF: Allow compiler to choose best way to construct a copy

With move semantics added to the language and the standard library updated with
move constructors added for many types it is now interesting to take an
argument directly by value, instead of by const-reference, and then copy. This
check allows the compiler to take care of choosing the best way to construct
the copy.

The transformation is usually beneficial when the calling code passes an rvalue
and assumes the move construction is a cheap operation. This short example
illustrates how the construction of the value happens:

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-pass-by-value  -header-filter=.* -fix

src/lib_json/json_reader.cpp

@@ -88,9 +88,8 @@ bool Reader::containsNewLine(Reader::Location begin, Reader::Location end) {
 // //////////////////////////////////////////////////////////////////
 
 Reader::Reader()
-    : errors_(), document_(), begin_(), end_(), current_(), lastValueEnd_(),
-      lastValue_(), commentsBefore_(), features_(Features::all()),
-      collectComments_() {}
+    : errors_(), document_(), commentsBefore_(), features_(Features::all())
+      {}
 
 Reader::Reader(const Features& features)
     : errors_(), document_(), begin_(), end_(), current_(), lastValueEnd_(),