v0.31.0-rc3

In this version:

• The WDLDrawRateTarget option now accepts the value 0 (new default) to retain raw WDL values if WDLCalibrationElo is set to 0 (default).
• Improvements to the verbose move stats if `WDLEvalObjectivity is used.
• The centipawn score is displayed by default for old nets without WDL output.
• Some build system improvements.