Rename pawn chain to connected

The flag raises also in case of a pawn duo, i.e.
when we have two adjacent pawns on the same rank,
and not only in case of a chain, i.e. when the two
pawns are on a diagonal line.

See this for a reference:
http://en.wikipedia.org/wiki/Connected_pawns

Renaming suggested by Ralph.

No functional change.
Simplify move_importance()

Drop a useless parameter. This works because ratio1 and ratio2
are ratios of linear combinations of thisMoveImportance and
otherMovesImportance and so the yscale cancels out.

Therefore the values of ratio1 and ratio2 are independent
of yscale and yscale can be retired.

The same applies to yshift, but here we want to ensure
move_importance() > 0, so directly hard-code this safety
guard in function definition.

Actually there are some small differences due to rounding errors
and usually are at most few millisecond, that's means below 1% of
returned time, apart from very short intervals in which a difference
of just 1 msec can raise to 2-3% of total available time.

No functional change.
Further simplify move_importance()

Function move_importance() is already always
positive, so we don't need to add a constant
term to ensure it.

Becuase move_importance() is used to calculate
ratios of a linear combination (as explained in
previous patch), result is not affected. I have
also verified it directly.

No functional change.
Simplify move_importance(): take 3

Use pow() of a negative number instead of 1/x

No functional change.
Update copyright year

No functional change.
Scale eval when down to only one pawn

Passed both short TC
LLR: 2.97 (-2.94,2.94) [-1.50,4.50]
Total: 11921 W: 2346 L: 2208 D: 7367

And long TC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 21002 W: 3395 L: 3197 D: 14410

bench: 7602383
Ensure move_importance() is non-zero

In case ply is very high, function will round
to zero (although mathematically it is always
bigger than zero). On my system this happens at
movenumber 6661.

Although 6661 moves in a game is, of course,
probably impossible, for safety and to be locally
consistent makes sense to ensure returned value
is positive.

Non functional change.
Remove duplicated code

Introduce update_stats() and remove correspondng
duplicated code.

No functional change.
Fix a typo

Spotted by Isaac H. Dunn.

No functional change.
Tweak King PST tables

First tested with 50K games at very short TC of 5+0.05
ELO: 3.11 +-2.0 (95%) LOS: 99.9%
Total: 49665 W: 10941 L: 10497 D: 28227

Then retested with usual SPRT at short TC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 16875 W: 3198 L: 3049 D: 10628

And at long TC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 5890 W: 985 L: 857 D: 4048

bench: 7800379
Assorted grammar fixes

Mainly from Lyudmil Antonov and
one from Henri Wiechers and Louis Zulli.

No functional change.
Retire grain size code

Seems useless at long TC.

Tested at 60+0.05
ELO: 2.98 +-2.2 (95%) LOS: 99.6%
Total: 30440 W: 4934 L: 4673 D: 20833

And at 120+0.05
ELO: 2.50 +-2.6 (95%) LOS: 97.1%
Total: 19633 W: 2848 L: 2707 D: 14078

bench: 8502826
Stop earlier if iteration is taking too long

If we are still at first move, without a fail-low and
current iteration is taking too long to complete then
stop the search.

Passed short TC:
LLR: 2.97 (-2.94,2.94) [-1.50,4.50]
Total: 26030 W: 4959 L: 4785 D: 16286

Long TC:
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 18019 W: 2936 L: 2752 D: 12331

And performed well at 40/30
ELO: 4.33 +-2.8 (95%) LOS: 99.9%
Total: 20000 W: 3480 L: 3231 D: 13289

bench: 8502826
Retire easy move

Remove the easy move code and add the condition to
play instantly if only one legal move is available.

Verified there is no regression at 60+0.05
ELO: 0.17 +-1.9 (95%) LOS: 57.0%
Total: 40000 W: 6397 L: 6377 D: 27226

bench: 8502826
Fix early stop condition

While editing original Uri's messy patch
I have incorrectly simplified the logic
condition. Here is the correct original
version, as it was tested.

bench: 8502826
Position::gives_check - use ci.ksq

Also remove a couple of local variables while
there.

No functional change.
Rename Position::hidden_checkers to check_blockers

No functional change.
Retire KBBKN endgame

As pointed out by Joona, Lucas and otehr people in
the forum, this endgame is not a known, there are many
positions where it takes more than 50 moves to claim the
win and becasue exact rules is not possible better to
retire and allow the search to workout the endgame for us.

bench: 8502826
Ad-hoc shelter rule

This hacky rule allows to get an about right eval out of this position:
r2qk2r/ppp2p2/2npbn2/2b1p3/2P1P1P1/2NB1PPp/PPNP3K/R1BQ1R2 b kq - 0 13

And, more importantly, passed both short TC:
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 6239 W: 1249 L: 1127 D: 3863

And long TC:
LLR: 2.96 (-2.94,2.94) [0.00,6.00]
Total: 38371 W: 6165 L: 5888 D: 26318

bench: 8183238
Introduce 'follow up' moves

When we have a fail-high of a quiet move, store it in
a Followupmoves table indexed by the previous move of
the same color (instead of immediate previous move as
is in countermoves case).

Then use this table for quiet moves ordering in the same
way we are already doing with countermoves.

These followup moves will be tried just after countermoves
and before remaining quiet moves.

Passed both short TC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 10350 W: 1998 L: 1866 D: 6486

And long TC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 14066 W: 2303 L: 2137 D: 9626

bench: 7205153