Nibbler::backN

- Added a method to support multi-byte backstep through a string.
- Added unit tests.

src/Nibbler.cpp

@@ -1077,6 +1077,18 @@ bool Nibbler::skipRx (const std::string& regex)
 }
 #endif
 
+////////////////////////////////////////////////////////////////////////////////
+bool Nibbler::backN (const int quantity /*= 1*/)
+{
+  if (_cursor >= quantity)
+  {
+    _cursor -= quantity;
+    return true;
+  }
+
+  return false;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 void Nibbler::getRemainder (std::string& result)
 {

src/Nibbler.h

@@ -93,6 +93,8 @@ public:
   bool skipRx (const std::string&);
 #endif
 
+  bool backN (const int quantity = 1);
+
   void getRemainder (std::string&);
 
   char next ();