feat: Set default legacy mode to false in DUI::addIncludePath

This changes the default value of the 'legacy' parameter in the
DUI::addIncludePath method to false. Since this API was just introduced,
it is preferred to use the new capabilities by preserving the left-to-right
order.

Author: jcfr

simplecpp.h

@@ -430,7 +430,7 @@ namespace simplecpp {
          *  If 'legacy' is true, the path is added to the 'includePaths' vector;
          *  otherwise, it is added to 'searchPaths' with 'PathKind::Include'.
          */
-        void addIncludePath(const std::string& path, bool legacy) {
+        void addIncludePath(const std::string& path, bool legacy=false) {
             if (legacy) {
                 includePaths.push_back(path);
             } else {