Remove undefended minors

Tested in "no regression" mode.

Passed both STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 68026 W: 12277 L: 12236 D: 43513

And LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 85682 W: 12861 L: 12836 D: 59985

bench: 7311935
Drop to qsearch at low depth in razoring

If razoring conditions are satisfied and
depth is low, then directly drop in qsearch.

Passed both STC
LLR: 2.98 (-2.94,2.94) [-1.50,4.50]
Total: 12914 W: 2345 L: 2208 D: 8361

And LTC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 50600 W: 7548 L: 7230 D: 35822

bench: 8739659
Extract a reliable PV line

Truncate the extracted PV from the point where
the score stored in hash starts to deviate from
the root score.

Idea from Ronald de Man.

bench: 8732553
Fix an off-by-one bug in extract_pv_from_tt

At root we start counting plies from 1,
instead pv[] array starts from 0. So
the variable 'ply' we use in extract_pv_from_tt
to index pv[] is misnamed, indeed it is
not the real ply, but ply-1.

The fix is to leave ply name in extract_pv_from_tt
but assign it the correct start value and
consequentely change all the references to pv[].
Instead in insert_pv_in_tt it's simpler to rename
the misnamed 'ply' in 'idx'.

The off-by-one bug was unhidden when trying to use
'ply' for what it should have been, for instance in
this position:

position fen 8/6R1/8/3k4/8/8/8/2K5 w - - 0 1

at depth 24 mate line is erroneusly truncated due
to value_from_tt() using the wrong ply.

Spotted by Ronald de Man.

bench: 8732553
Symmetric king safety

Retire current asymmetric king evaluation
and use a much simpler symmetric one.

As a side effect retire the infamous
'Aggressiveness' and 'Cowardice' UCI
options.

Tested in no-regression mode,

Passed both STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 33855 W: 5863 L: 5764 D: 22228

And LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 40571 W: 5852 L: 5760 D: 28959

bench: 8321835
Update polyglot.ini after last patch

No functional change.
Add perft 'divide' command

To show perft numbers for each move. Just
use 'divide' instead of 'perft', for instance:

position startpos moves e2e4 e7e5
divide 4

Inspired by Ronald de Man.

No functional change.
Tidy up tt.h

Backport some non-functional changes
found working on 'dense TT' patch.

No functional change.
Fix a warning with Intel compiler

warning #2259: non-pointer conversion from
"int" to "int16_t={short}" may lose significant
bits.

No functional change.
Revert "Symmetric king safety"

Regression test of 40K games at 60 secs shows
this commit to be a 2-3 ELO regression.

So revert to original king safety.

bench: 8732553
Stockfish 5

Stockfish bench signature is: 8732553
Restore development version

bench: 8732553
Retire polyglot.ini

All actively maintained GUI are able
to understand UCI protocol, so there
is no more need for this obsolete file.

No functional change.
Retire eval weights UCI options

There is really little that user can achieve (apart
from a weakened engine) tweaking these parameters
that are already tuned and have no immediate or visible
effect.

So better do not expose them to the user and avoid the
typical "What is the best setup for my machine?" kind of
question (by far the most common, by far the most useless).

No functional change.
Retire Polyglot Book management

Book handling belongs to GUI, we kept this code
for historical reasons, but nowdays there is
really no need of this old, (mostly) unused
and especially incorrect designed functionality.

It is up to the GUI to choose the book (far easier for
the user) and to select the book parameters. In no
place, including fishtest, TCEC, rating lists, etc.
the "own book" is used, moreover currently SF is
released without any book and even if in the future we
bundle a book in the release package, it will be the GUI
that will take care of it.

This corrects a wrong design decision that Galurung
and later Stockfish inherited from what was common
practice many yeas ago.

No functional change.
Decrease reduction for moves that escape a capture

Passed both STC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 10094 W: 1833 L: 1704 D: 6557

and LTC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 27738 W: 4147 L: 3928 D: 19663

bench : 8599236
Add some const qualifier

No functional change.
Use see() instead of see_sign() in previous patch

Before it was working by accident in case of
see_sign() and failing with see() due to how
castle moves are coded (king captures the rook).

Better to explicitly filter out castling moves
and use see() without any surprise/trick.

No functional case.
Symmetric King Safety: take 2

Another attempt at retiring current asymmetric
king evaluation and use a much simpler symmetric
one. As a good side effect we can avoid recalculating
eval after a null move.

Tested in no-regression mode and passed

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 21580 W: 3752 L: 3632 D: 14196

LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 18253 W: 2593 L: 2469 D: 13191

And a LTC regression test against SF DD to
verify we don't have regression against
weaker engines due to some kind of 'contempt'
effect:

ELO: 54.69 +-2.1 (95%) LOS: 100.0%
Total: 40000 W: 11072 L: 4827 D: 24101

bench: 8205159
Update Readme.md

Retire line about polyglot.ini and
book as they are not used anymore.

No functional change.