explaining of "what a C string is", and make it more clear that these
functiosn BEHAVE EXACTLY LIKE snprintf with "%s"!  (anyone who wants
to write a 'strlcpy considered harmful' paper should probably write a
'strlcpy and snprintf considered harmful' paper instead).
note to those from other projects reading this commit message: It would
be very good if this new manual was picked up in your project.
ok jmc millert krw