v0.27.0-rc2

• Fix additional cases where 'invalid move' could be incorrectly reported.
• Replace WDL softmax in cudnn backend with same implementation as cuda
  backend. This fixes some inaccuracy issues that were causing training
  data to be rejected at a fairly low frequency.
• Ensure that training data Q/D pairs form valid WDL targets even if there
  is accumulated drift in calculation.
• Fix for the calculation of the 'best q is proven' bit in training data.
• Multiple fixes for timelosses and infinite instamoving in smooth time
  manager. Smooth time manager now made default after these fixes.