Remove redundant condition in probcut

When !ss->skipNullMove it is assured that excludedMove == MOVE_NONE

No functional change.
Merge some if statements in pos_is_ok()

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Remove confusing optimization

Here we skip the call to pos.attacks_from<ROOK>(s) in the 98%
of cases, testing the first 2 members first. Unfortunatly
code is a bit triky and not clear. So we give up to the
speed optimization in exchange of more code clarity.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Include file attacks in 'major on pawn'

Passed both short TC:
LLR: 2.97 (-2.94,2.94)
Total: 57846 W: 12248 L: 11974 D: 33624

And long one:
LLR: 2.95 (-2.94,2.94)
Total: 9181 W: 1732 L: 1581 D: 5868

bench: 4609948
Micro-optimize perft

Avoid to call perft function when we just need to count
moves, at leaf nodes.

Speed up of almost 2%

No functional change.
Name functions along corresponding UCI commands

No functional change.
Simplify hidden_checkers()

De-templetize and pass color as function argument.
No speed change.

No functional change.
Retire ThisAndAdjacentFilesBB[]

It is unused. Also renamed attack_span_mask to
pawn_attack_span

No functional change.
Retire in_front_bb(Color c, Square s) overload

Explciitly call rank_of() in the few places where
it is used.

No functional change.
Don't explicitize enum values when not needed

Compiler will chose the correct values in sequential
order for you.

Also move file and rank bitboards definitions to
bitboard.h

No functional change.
Move SquareDistance[] to bitboard.cpp

No functional change.
Fix some stale comments

No functional change.
Revert "Increase threshold of fail-low after null for cut nodes"

This reverts commit 388e0479865f537a4960161fb5c0f58f362bb822.
Merge branch 'master' into null_cut
Asymmetric null search depth: increase with CUT nodes

bench: 3950890