Hexadecimal is consistently used as format to not bloat too much the
output but keep it readable.  This information is useful mainly for
debugging purposes with for example pg_waldump.

Author: Michael Paquier
Reviewed-by: Nathan Bossart, Dmitry Dolgov, Andres Freund, Álvaro
Herrera
Discussion: https://postgr.es/m/20180413034734.GE1552@paquier.xyz