Bug - Durations

- Duration were parsed as <int><unit> in A3, whereas <number><unit> is
  correct.
- Added Nibbler::str method for internal access.
- Nibbler::save, ::restore now return positions.  Useful for extracting
  substrings.
- Modified countdown.t to use the (now) correct units for durations.

src/Nibbler.cpp

@@ -1116,15 +1116,21 @@ std::string Nibbler::next (const int quantity)
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-void Nibbler::save ()
+std::string::size_type Nibbler::save ()
 {
-  mSaved = mCursor;
+  return mSaved = mCursor;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-void Nibbler::restore ()
+std::string::size_type Nibbler::restore ()
 {
-  mCursor = mSaved;
+  return mCursor = mSaved;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+const std::string& Nibbler::str () const
+{
+  return mInput;
 }
 
 ////////////////////////////////////////////////////////////////////////////////