Changes

Implemented ponder support.
Tablebases are supported now (only WDL probe for now).
Command line parameter is
--syzygy-paths=/path/to/syzygy/
Old smart pruning flag is gone. Instead there is --futile-search-aversion flag.
--futile-search-aversion=0 is equivalent to old --no-smart-pruning.
--futile-search-aversion=1 is equivalent to old --smart-pruning.
Now default is 1.47, which means that engine will sometimes decide to stop search earlier even when there is theoretical chance (but not very probable) that best move decision could be changed if allowed to think more.
Lc0 now supports configuration files. Options can be listed there instead of
command line flags / uci params.
Config should be named lc0.config and located in the same directory as lc0.
Should list one command line option per line, with '--' in the beginning being optional, for example:

syzygy-paths=/path/to/syzygy/
In uci info, "depth" is now average depth rather than full depth (which was 4 all the time).
Also, depth values do not include reused tree, only nodes visited during the current search session.
--sticky-checkmates experimental flag (default off), supposed to find shorter checkmate sequences.
More features in backend "check".

Release windows executables are built with "whole program optimization".
Added --out-of-order-eval flag (default is off).
Switching it on makes cached/terminal nodes higher priority, which increases nps.
OpenCL backend now supports batches (up to 5x speedup!)
Performance optimizations for BLAS backend.
Total visited policy (for FPU reduction) is now cached.
Values of priors (P) are stored now as 16-bit float rather than 32-bit float, that saves considerable amount of RAM.

Fixed en passant detection bug which caused the position after pawn moving by two squares not counted towards threefold repetition even if en passant was not possible.
Fixed the bug which caused --cache-history-length for values 2..7 work the same as --cache-history-length=1.
This is fixed, but default is temporarily changed to --cache-history-length=1 during play. (For training games, it's 7)

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