WIP: Resolve "VectorComposite::getStructure() sorted string"

Closes #349

include/core/state_block/state_composite.h

@@ -25,6 +25,9 @@ typedef std::string StateStructure;
 typedef std::unordered_map < char, StateBlockPtr   > StateBlockMap;
 typedef StateBlockMap::const_iterator StateBlockMapCIter;
 
+bool structcmp(const StateStructure& s1, const StateStructure& s2);
+
+
 class VectorComposite : public std::unordered_map < char, Eigen::VectorXd >
 {
     public: