Small tidy up in move_to_san

No functional change.
Some more work in pretty_pv

No functional change.
Sync some common names

No functional change.
Rescale UCI scores to PawnValueEg

This is more consistent with what other engines are doing.
Often people thinks that SF's scores are overblown. In the
end, it just boils down to the arbitrary way of rescaling them.

No functional change.