Changes

In order to allow the quiescence search to stabilize, we need to be able to stop searching without necessarily searching all available [[Captures|captures]]. In addition, we need a score to return in case there are no captures available to be played. This is done by a using the [[Evaluation|static evaluation]] as a "stand-pat" score (the term is taken from the game of poker, where it denotes playing one's hand without drawing more cards). At the beginning of quiescence, the position's evaluation is used to establish a [[Lower Bound|lower bound]] on the score. This is theoretically sound because we can usually assume that there is at least one move that can either match or beat the lower bound. This is based on the [[Null Move Observation]] - it assumes that we are not in [[Zugzwang]]. If the lower bound from the stand pat score is already greater than or equal to beta, we can return the stand pat score ([[Fail-Soft|fail-soft]]) or [[Beta|beta]] ([[Fail-Hard|fail-hard]]) as a [[Lower Bound|lower bound]]. Otherwise, the search continues, keeping the evaluated "stand-pat" score as an [[Lower Bound|lower bound]] if it exceeds [[Alpha|alpha]], to see if any [[Tactical movesMoves|tactical moves]] can increase [[Alpha|alpha]].