Since coefficients differ only in the last bit when writing to the
bitstream it was possible to remove the sign from the tables, thus
halving them. Also now all quantization is done in the unsigned domain
as the sign is completely separate, which gets rid of the need to do
quantization on 32 bit signed integers.

Overall, this slightly speeds up the encoder depending on the machine.
The commit still generates bit-identical files as before the commit.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>