Simplify a condition in is_KXK()

No functional change.
Small renaming in material weights

Also dropped some temporary variable: compiler
is more than able to push on stack temp values
by itself (verified).

No functional change.
Move game_phase() to Position

It seems a more natural to place this
function there.

No functional change.
Better value clipping in game_phase()

No functional change.
Add AUTHORS
Remove some duplicates
Ensure ttValue != VALUE_NONE in singular extension search

The assert:

  assert(ttValue != VALUE_NONE);

Could fire for multiple reasons (although is very rare),
for instance after an IID we can have ttMove != MOVE_NONE
while ttValue is still set at VALUE_NONE.

But not only this, actually SMP is a source of corrupted
ttValue and anyhow we can detect the condition:

 ttMove != MOVE_NONE && ttValue == VALUE_NONE

even north of IID.

Reported by Ronald de Man.

It is so rare that bench didn't change.

bench: 7710548
Some reformatting in pawns.cpp

No functional change.
Merge pull request #5 from glinscott/authors

Add AUTHORS
Scale down endgames with pawns on one or two adjacent files
Original version of shane's patch
Merge remote-tracking branch 'upstream/master' into ants_smp
Revert "Check for an available slave early on"

This reverts commit ce1c260ea97c14eea996d0a2638f4876ccbc412b.
Merge pull request #8 from glinscott/revert_ce1c260

Revert "Check for an available slave early on"
A bit more cleanup
Merge pull request #9 from glinscott/pawnspan

Scale down endgames with pawns on one or two adjacent files

Passed STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 16081 W: 2745 L: 2604 D: 10732

Passed LTC
LLR: 2.95 (-2.94,2.94) [1.00,6.00]
Total: 123832 W: 17292 L: 16584 D: 89956

128k games to measure ELO at 15+0.05:
ELO: 2.07 +-1.1 (95%) LOS: 100.0%
Total: 128000 W: 21632 L: 20869 D: 85499

New bench: 8028792
Merge remote-tracking branch 'upstream/master' into ants_smp