close #32

reallocarray introduction available on glibc 2.26. allocates an array of m*n elements but checking for overflow.

those functions differently than the strn* ones as
they do not pad with zero to remaining bytes but guarantees
a null terminator.

BufWriter has more capacity (8k vs 1k) and doesn't flush the stream after '\n'.
That change helps to reduce the number of syscalls, especially when dealing with text files.

Since BufWriter has a different way of getting number of pending elements than LineWriter -
Pending trait was introduced to deal with that.

inner_scanf prematurely exited before parsing collected string