Update Readme.md

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

No functional change.
Fix a warning with MSVC Premium 2013

Reported by Ron Britvich.

No functional change.
Revert "Score extractors"

Are broken for big-endian case and
I have verified with MSVC 2013 Premium
bench is correct and there is no
miscompilation, so the main reason
to change the original code drops.

No functional change.