crit: Beautify unix names recode

Unix socket name can be a string with any bytes in it. So to
print the name we use base64 encoding. Doing so doesn't allow
to see the socket name when it contains only printable chars.

So here's the custom encoding for bytes fields, that can be
used for custom conversion.

Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>