added Path::join utility method

src/core/filesystem.cpp

@@ -133,4 +133,9 @@ FilePath Path::normalize(const FilePath& path)
 	}
 
 	return normalized;
+}
+
+FilePath Path::join(const FilePath& a, const FilePath& b)
+{
+	return normalize(FilePath(a).append("/").append(b));
 }