switched from gthread to pthread

Because gthread is giving me warnings and pthread is quite universal
anyways.
debian package does not really build-depends on automake
fixed filtration.h variables to be extern

Not sure how I managed to miss it earlier.
include vector.h into filtration.h

Because we're using struct vector
avoid array of 0 elements

Which upsets clang's sanitizer
do not allow negative indexes for char tables

Because char can be signed
declare prepare_scorer()

Which is used by main.c
include sys/wait.h for waitpid
unbreak arrow keys handling