[Patch v3] util: add gzreadline

[David Bremner]

Tomi Ollila <tomi.ollila at iki.fi> writes:

> "On error, gzgets() shall return Z_NULL.
>
> In light of this I'd say no. can we set out-of-memory using some public
> api so it is available using gzerror()
>
>

Since we already "broke" the API, what about

1) start a "util_status_t" enum, later unify that with the hex_ return codes.

2) 

util_status_t
gz_getline (void *ctx, char **buf, size_t *bufsize, ssize_t *bytes_read,
           gzFile stream);

d