MINOR: standard: The parse_binary() returns the length consumed and his documentation...

MINOR: standard: The parse_binary() returns the length consumed and his documentation is updated

Actually the values returned by this function is never used. All the
callers just check if the resultat is non-zero. Before this patch, the
function returns the length of the produced content. This value is not
useful because is returned twice: the first time in the return value and
the second time in the <binstrlen> argument. Now the function returns
the number of bytes consumed from <source>.