lib/tt: count read cells, improve \x?? hex encoding

lib/tt: count read cells, improve \x?? hex encoding

 * use wcwidth() to count real number of columns required for
   multibyte strings

 * encode control characters with \x?? in raw and export (NAME=data) outputs

 * use \x?? for controls and non-printable characters in the default outputs

 * use \x?? to encode already existing hex sequences, for example

	/mnt/ugly\x20space  --->  /mnt/ugly\x5cx20space

   this is not used in the default output, but in raw/export outputs
   only (which is designed for scripts).

Signed-off-by: Karel Zak <kzak@redhat.com>