Enhancement - ID and sequences

- The first ID added as a sequence is accessible through the original
  T::getId and T::setId interface.
- An ID added via T::getId is accessible as the first ID in a sequence.
- Allows some commands to operate exclusively with sequences, and others
  with a single ID.

src/T.cpp

@@ -588,8 +588,6 @@ void T::parse (const std::string& line)
                 openAttrBracket + 1, closeAttrBracket - openAttrBracket - 1);
               std::vector <std::string> pairs;
               split (pairs, attributes, ' ');
-              if (pairs.size () == 0)
-                throw std::string ("Could not find any attributes.");
 
               for (size_t i = 0; i <  pairs.size (); ++i)
               {