Go 1.10 improved the way of passing strings between C and Go
with https://go-review.googlesource.com/c/go/+/70890
This change adapts API/helpers to a new convention,
without changing existing API surface and without benefiting
from a new way of passing strings.
Another, perferable on my readind of `go doc cgo`, but
more invasive approach would be to change ALL enry C API to
always return *C.char \w C.CString()
Signed-off-by: Alexander Bezzubov <bzz@apache.org>
