WISH: add more getters/setter for image! type, not just RGB and ALPHA

[Oldes]

I often need to create image from foreign data and these data are usually not in two binaries which Rebol is now using to describe an image (RGB and ALPHA). I think that there should be possible to use this to get the binaries from an image:

i: make image! 1x1 i/1: 1.2.3.100
i/rgba ;== #{01020364}
i/rgbo ;== #{0102039B}
i/argb ;== #{64010203}
i/orgb ;== #{9B010203}
i/bgra ;== #{03020164}
i/bgro ;== #{0302019B}
i/abgr ;== #{64030201}
i/obgr ;== #{9B030201}
i/opacity ;== #{9B}
i/alpha   ;== #{64}

.. and also be able to set these. Now it is possible only with: i/rgb: #{050607}

Having also variant with premultiplied alpha would be also useful in many cases.