Calculate maximum threat for hanging pieces

Use the max_threat() helper function to estimate more precisely the
best hanging piece threat.  Also retunes the Threat array using SPSA.

STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 7598 W: 1596 L: 1468 D: 4534

LTC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 7896 W: 1495 L: 1350 D: 5051

Bench: 6816504

Resolves #73
Reformat max_threat()

Helper function should just know how to find the
biggest piece type in a bitboard. All the threat
logic and data shoud be in evaluate_threats().

This nicely separates the scope of the two functions
in a more consistent way and simplifies the code.

No functional change.
Retire to_char() helpers

Remove some useless wrappers and make
the conversion explicit and starightforward.

No functional change.
Rename ucioption.h to uci.h

We are going to add all UCI related
functions here, so first rename it
to a more proper name.

No functional change.
Retire notation.h

And move the few remaining content
under UCI namespace where they belong.

No functional change.
Final UCI helpers renaming

To reflect new changes, specifically that
now are all under UCI namespace.

No functional change.
Retire notation.cpp

Now we can finally retire notation.cpp
and move UCI helpers under uci.cpp

No functional change.
Fix an obscure gcc warning

warning: narrowing conversion from ‘int’ to ‘char’ inside { }
is ill-formed in C++11 [-Wnarrowing]

When pedantic meets esoteric!

No functional change.
Improve compatibility with Shredder Classic GUI

This commit fixes two issues:

1) Don't print PVs after the search has been interrupted

    This solves the "mate 0 upperbound" scores that sometimes
    creep up when a multi-PV analysis gets interrupted with
    the `stop` command.

2) Print multipv before score

    Shredder Classic fails to identify the main PV
    (the one with multipv 1) if `score` comes first.
    This leads to an eval graph that doesn't reflect
    the scores actually reported by Stockfish when
    doing a multiPV analysis.

No functional change

Closes #76
Tune PawnsFileSpan

Passed the following SPRT tests:

STC:
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 24428 W: 5056 L: 4880 D: 14492

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 26590 W: 4715 L: 4472 D: 17403

Bench: 6615949

Resolves #78
Speed up max_piece_type()

Write code in the way that allows compiler to perform loop unrolling.

My measurement (32 cycles each):

Orig:

Time (Mean: 2466.59375, Trimmed mean: 2464.25, Std: 12.6869487803348)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1741.09247987678, Trimmed mean: 1742.72879715475, Std: 8.93612608292678)

Time (Mean: 2470.15625, Trimmed mean: 2468.75, Std: 12.7484581610433)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1738.58176151341, Trimmed mean: 1739.54618465403, Std: 8.95585822316946)

Mod:

Time (Mean: 2449.90625, Trimmed mean: 2445.9375, Std: 12.1000116635508)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1752.94829372932, Trimmed mean: 1755.75934908231, Std: 8.61478453124504)

Time (Mean: 2442.78125, Trimmed mean: 2441.1875, Std: 8.17839157228837)
Nodes (Mean: 4294458, Trimmed mean: 4294458, Std: 0)
Speed (Mean: 1758.03872783803, Trimmed mean: 1759.16825356261, Std: 5.81131316346191)

No functional change
A small clean up of previous patch suggested by Marco

No functional change
max_piece_type cleanup, and slight speed increase.

No functional change.

Resolves #81
Code style clean-up

This piece of code needs some love.

No functional change.
Merge pull request #82 from official-stockfish/clean_up_bishop_code

Code style clean-up

No functional change.
Prefer operator<<() to pretty()

It is more idiomatic, we didn't used it
in the past because Position::pretty(Move)
had a calling argument, but now we can.

As an added benefit, we avoid a lot of string
copies in the process because now we avoid
std::ostringstream ss.

No functional change.
Remove dead code

No functional change.

Closes #87
Consistent use of anonymous namespace

Objects that are only accessible at file-scope should be put in the anonymous namespace.
This is what the  C++ standard recommends, rather than using static, which is really C-style and results in static linkage.

Stockfish already does this throughout the code. So let's weed out the few exceptions,
because... they have no reason to be exceptional.

No functional change.

Resolves #84
Correctly describe POPCNT compile

SSE4.2 has nothing to do with POPCNT. We must dispell this myth, because
Stockfish is a reference and many will copy this mistake if they see it in Stockfish:
* SSE is an SIMD instruction set, relative to vectorization (using special 128-bit registers).
* POPCNT/LZCNT work on normal registers (eg. AL, AX, EAX, RAX).

The confusion comes from the fact that, in the Intel product line, it just
so happens that SSE4.2 and POPCNT/LZCNT came out at the same time. But this
is not true for AMD. For example, all AMD Pheniom II have SSE3 but no
POPCNT/LZCNT, and that is why the modern compile uses  -msse3 -popcnt and not -msse4.2.

No functional change.

Resolves #86
Retire PawnsFileSpan

It is useless. Tested as no regression:

STC
LLR: 4.06 (-2.94,2.94) [-3.00,1.00]
Total: 140718 W: 28527 L: 28568 D: 83623

LTC
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 60034 W: 10359 L: 10303 D: 39372

bench: 6564212

Resolves #88