Fails to compile on my PGI compiler

[ttvd]

Hello,

I ran into an issue recently, lent uses #pragma once which is not supported on my current PGI compiler, unfortunately.

Can we add include guards? Would you accept a pull request?

Thanks,

PS. Awesome library!

[nem0]

Hi ttvd,

Thanks, I spent many many sleepless minutes making this library. It was a painful process but in the end I think the result speaks for itself.

I will add guards in a minute.

XOXO,
Nem0

[nem0]

Fixed via 40e2101