DESCRIPTION: Add some sentences giving an overview of these interfaces.
Add note recommending use of malloc(3).
Change name of brk() argument to the simpler 'addr'.
Add "(void *)" cast to "-1" for error return of sbrk().
Removed some incorrect text about "brk(0)".
Note that SUSv2 specified the return value of sbrk().
Added a detail on the glibc brk() wrapper.
Remove discussions of standards old (C89 and POSIX.1-1990);
CONFORMING TO already discusses the situation with respect
to more recent standards.
and point out that the glibc brk() wrapper provides different behaviour.
Note that sbrk() is implemented as a library function in glibc that
calls the brk() system call.