Special buffer for caching passes

[cansik]

For effects like bloom it would be nice to have a special buffer to store textures and information.

[cansik]

Maybe this is not needed. It is possible to work with two buffers to create multipass effects. See an example here:

https://github.com/cansik/processing-postfx/blob/master/src/main/java/ch/bildspur/postfx/pass/BloomPass.java#L43-L95