Added an empty constructor to INIReader

Adds more flexibility, allows initialising INIReader after declaration.
diff --git a/INIReader.h b/INIReader.h
index b425bb2..68c3dc3 100644
--- a/INIReader.h
+++ b/INIReader.h
@@ -312,6 +312,9 @@
 class INIReader
 {
 public:
+    // Empty Constructor
+    INIReader() {};
+  
     // Construct INIReader and parse given filename. See ini.h for more info
     // about the parsing.
     INIReader(std::string filename);