Custom PPSSPP shaders

[guest.r]

Cheer up m8.

If you need an aa 4.o shader with scanlines i could make you one, so you can use the Reshade preset as before with RA.

Otherwise overgrown shaders don't work like real multipass shaders, so the results would not be as expected here.

Meanwhile i put together some crt shaders. Since the input resolution is a bit larger than used they should look better on 1440p for example.

Shaders have lots of options included, i think there should be no problems in altering some of them.

Included are:

- crt lottes - the classic
- crt hyllian - very nice crt shader
- crt easymode - the mighty newcomer (OpenGL only)
- crt lottes tv - kinky tv color aberrations, screen cushion

Edit: small changes, thanks to Luna for fixing the mask code.