The great type cleanup: Use C99 types where applicable.

The great type cleanup: Use C99 types where applicable.

LibUCW types (u16 and friends) are now based on the C99 <stdint.h> types.

Old-style sbyte, word, sword and addr_int_t are gone (I've removed all refs
to them in the previous commits).

<stddef.h> is now included automatically, bringing types like size_t and
also NULL.

The operations on pointers (GET_P, PUT_P etc.) have been removed from
lib/config.h as nobody uses them and bgetp() is just a duplicate of bgeta()
from lib/fastbuf.h. BYTES_PER_P is gone as well.

#define _GNU_SOURCE had to be moved to lib/config.h, where it belongs anyway.