0.15.2

A small UCI fix on top of 0.15.1.

Fixes

• go ponder and ponderhit no longer throw. go ponder searches like go infinite: the clock that comes with it is the opponent's time and doesn't limit the search, and bestmove is held until stop or ponderhit. ponderhit ends the search and plays the move found so far at once, so the engine can't lose time on it. Real pondering, continuing the search on our own clock, is still to come, the Ponder option isn't advertised so GUIs don't start pondering on their own.

No change to search or evaluation, same bench as 0.15.1.

Binaries as before: Windows & Linux, x86-64, x86-64-v2 (POPCNT, SSE4.2) and x86-64-v3 (AVX2, BMI2).

Bench 506783 nodes.