Clarify relationship of MIN with VMIN and TIME with VTIME.
Noted that CIBAUD, OFDEL, and DELECHO are not implemented on Linux.
Added explanatory paragraph for phrases "not in POSIX" and
"XSI".
Clarify speed argument for cfsetispeed() text.
Note that LOBLK is not implemented on Linux.
Clarify arguments for cfsetspeed().
Various formatting changes
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'.