https://ftp.pwg.org/pub/pwg/ipp/wd/wd-pwgsafegcode10-2019318.pdf

Printer Description attributes:	Reference
------------------------------	---------
pwg-safe-gcode-supported (1setOf text(MAX))	[SAFEGCODE]

https://ftp.pwg.org/pub/pwg/informational/bp-pwgsafegcode10-20190604.pdf

Printer Description attributes:	Reference
------------------------------	---------
pwg-safe-gcode-supported (1setOf text(MAX))	[SAFEGCODE]

Fix link to PWG Safe G-Code BP.
Fix link to PWG Safe G-Code BP.
