Adding Ptex for OIIO?

[boberfly]

Hey John,

Could we perhaps sneak-in Ptex for OIIO?
https://github.com/wdas/ptex/archive/v2.3.2.tar.gz

I can whip up a config for this if you'd like. I'm using Gaffer's OIIO for Cycles' image reading services and Cycles supports Ptex (and a stepping stone for me to try out that Moana scene).

Cheers!