Rename inner scope variables to differ from outer scope

These variables with the same name are not the same variables because of
scope rules.  While the compiler is not confused by this naming, it may
be less readable by someone attempting to edit this code.

Signed-off-by: Sean Robinson <[email protected]>

include/argparse/argparse.hpp

@@ -453,18 +453,18 @@ class Argument {
 
       struct action_apply {
         void operator()(valued_action &f) {
-          std::transform(start, end, std::back_inserter(self.mValues), f);
+          std::transform(first, last, std::back_inserter(self.mValues), f);
         }
 
         void operator()(void_action &f) {
-          std::for_each(start, end, f);
+          std::for_each(first, last, f);
           if (!self.mDefaultValue.has_value()) {
             if (auto expected = self.maybe_nargs())
               self.mValues.resize(*expected);
           }
         }
 
-        Iterator start, end;
+        Iterator first, last;
         Argument &self;
       };
       std::visit(action_apply{start, end, *this}, mAction);