Update FEATURES.md

Introduced text for `fix-1956-1977-1981` and `fix-1999`

FEATURES.md

@@ -2,7 +2,11 @@
 
 ## Code changes
 
+When primal infeasiblity is detected in presolve, no dual ray is available so, previously, the `has_dual_ray` parameter of `Highs::getDualRay` returned false and that was it. Now, if a null pointer is not passed for `dual_ray_value`, `Highs::getDualRay` will compute a dual ray - at the cost of solving the feasiblility LP without presolve. The same is now true for `Highs::getPrimalRay`. `Highs::getDualUnboundednessDirection` has been introduced to determine the product between the constraint matrix and the dual ray, forcing the calculation of the latter if necessary. Once a dual ray is known for the incumbent model in HiGHS, subsequent calls to `Highs::getDualRay` and `Highs::getDualUnboundednessDirection` will be vastly cheaper
 
+The method `Highs::getDualObjectiveValue` now exitsts to compute the dual objective value, returning `HighsStatus::kError` if it is not possible.
+
+The method `Highs::getStandardFormLp` now exists to return the incumbent LP in standard form - overlooking any integrality or Hessian. To determine the sizes of the vectors of data, the method is called without specifying pointers to the data arrays.