remove .gitignore
This file does not belong in the repository, but rather locally. Everyone uses different tools, and may want to tell git not to track differennt files.
add GPL headers
use GCC's vector arithmetic
* elegant high-level coe to manipulate eval = (opening, endgame) as vectors.
* translates into fast assembly code, using SIMD instruction set.

No function change: printed out both PST into files and diff-ed them to verify.
Merge branch 'master' into makemove
Make eval_t work on clang

Clang doesn't support scaler*vector operations for vectors defined using
vector_size, but it does if you use ext_vector_type. Unfortuately this
doesn't seem to work using GCC, so we need to use a different version for
the two different compilers. Annoying.