A number of small changes.

1. Add a move constructor to NumericDiffCostFunction, DynamicAutoDiffCostfunction
   and DynamicNumericDiffCostFunction.
2. Add optional ownership of the underlying functor.
3. Update docs to reflect this as well as the variadic templates that allow an
   arbitrary number of parameter blocks.

Change-Id: I57bbb51fb9e75f36ec2a661b603beda270f30a19

include/ceres/numeric_diff_cost_function.h

@@ -192,7 +192,10 @@ class NumericDiffCostFunction : public SizedCostFunction<kNumResiduals, Ns...> {
     }
   }
 
-  ~NumericDiffCostFunction() {
+  explicit NumericDiffCostFunction(NumericDiffCostFunction&& other)
+      : functor_(std::move(other.functor_)), ownership_(other.ownership_) {}
+
+  virtual ~NumericDiffCostFunction() {
     if (ownership_ != TAKE_OWNERSHIP) {
       functor_.release();
     }