SNES (and related) support

[robin-raymond]

Some notes for the future:
https://mrclick.zophar.net/TilEd/download/consolegfx.txt
https://wiki.superfamicom.org/transparency
https://megacatstudios.com/blogs/retro-development/super-nintendo-graphic-guide
https://en.wikibooks.org/wiki/Super_NES_Programming/Graphics_tutorial
https://megacatstudios.com/blogs/retro-development/snes-development-starting-from-scratch
https://en.wikibooks.org/wiki/Super_NES_Programming/pixel_editing_tutorial
https://www.youtube.com/watch?v=kwAjG2dj5ZM

Related to
#8

[robin-raymond]

https://megacatstudios.com/blogs/retro-development/super-nintendo-graphics-read-in-the-voice-of-brendan
https://snes.nesdev.org/wiki/Backgrounds
https://wiki.superfamicom.org/backgrounds
https://forums.nesdev.org/viewtopic.php?t=13610 [direct color]
https://wiki.superfamicom.org/palettes
https://megacatstudios.com/blogs/retro-development/metatiles
https://georgjz.github.io/snesaa01/
https://megacatstudios.com/ru/blogs/retro-development/creating-nes-graphics
https://megacatstudios.com/blogs/retro-development/game-development-lessons-from-retro-platforms
https://en.wikibooks.org/wiki/Super_NES_Programming/Super_FX_tutorial
https://therealmjp.github.io/posts/adventures-in-retro-development-snes-edition/
https://en.wikibooks.org/wiki/Super_NES_Programming/SNES_memory_map
https://en.wikibooks.org/wiki/Super_NES_Programming
https://georgjz.github.io/snesaa03/
https://megacatstudios.com/blogs/retro-development/creating-nes-art
https://megacatstudios.com/blogs/retro-development/sega-genesis-mega-drive-vdp-graphics-guide-v1-2a-03-14-17
https://www.gamedeveloper.com/design/as-snes-turns-25-devs-discuss-its-7-greatest-graphics-innovations

[robin-raymond]

Note: SNES is LSB (least significant bit) stored. Each bit of the bit plane is stored with the least significant bit in the first bit-plane. The next more significant bit is in the next bit plane (and so on).

https://docs.rs/snes-bitplanes/latest/snes_bitplanes/

Each tile is (normally) 8x8 pixels. The data is stored in bitplanes. Each row of the tile fills 1 byte, with the leftmost pixel being in bit 7.

Thus the highest bit is the left most pixel.

https://sneslab.net/wiki/Graphics_Format

[robin-raymond]

Export of SNES now added in #34

[robin-raymond]

This is now merged so feel free to provide feedback since the binary output is untested. Hopefully it's correct but probably it has some issues (especially given the nature of the bit plane encodings).