Global change to many pages...

Global change to many pages...
Various pages use inconsistent terms for 'null byte' (which
is the C99/SUSv3 term for the '\0' character).
To rectify this the following changes were made in these pages:

Replace 'zero byte' with 'null byte'.
Replace 'null character' with 'null byte'.
Replace 'nulls' with 'null bytes'.
Replace 'NUL-terminated' by 'null-terminated'.
Replace 'NUL' by 'null byte'.
Replace 'terminating NUL' by 'terminating null byte'.
Replace 'final NUL' by 'terminating null byte'.
Replace 'NUL character' by 'null byte'.