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)
 {