corrected usage instructions, made EnumerateCosts return a string ins…

…tead of printing to std::cout

src/toolkit/facility_cost.cc

@@ -17,8 +17,11 @@ FacilityCost::FacilityCost(double capital_cost) {
 
 FacilityCost::~FacilityCost() {}
 
-void FacilityCost::EnumerateCosts(){
-    std::cout<<capital_cost_<<std::endl;
+std::string FacilityCost::EnumerateCosts(){
+    std::ostringstream strs;
+    strs << capital_cost_;
+    std::string costs = strs.str();
+    return costs;
 }
 
 }  // namespace toolkit

src/toolkit/facility_cost.cycpp.h

@@ -2,6 +2,8 @@
 /// One should only need to:
 /// - '#include "toolkit/facility_cost.cycpp.h"' in the header of the 
 ///    archetype class (as private)
+/// - '#include "toolkit/facility_cost.h"' in the main include section
+///    of the header of the archetype class.
 
 cyclus::toolkit::FacilityCost cost;
 

src/toolkit/facility_cost.h

@@ -29,7 +29,7 @@ class FacilityCost {
   /// The default destructor for FacilityCost
   ~FacilityCost();
 
-  void EnumerateCosts();
+  std::string EnumerateCosts();
 
  private:
   /// Capital cost of the facility