Add fix for line search termination condition
Description
One of the search termination conditions in more_thuente_line_search.hpp
incorrectly computed a relative floating point delta for non-positive values because it did not use absolute values. In addition, the relative check behaves in likely inappropriate ways for values near zero because it only considers relative deltas.
How to Reproduce
The bug is in the code logic; it's unknown if this has or does result in reproducible incorrect behavior.
Current Behavior
(see above)
Expected behavior
(see above)