WIP: Big endian support and basic raw UDP framebuffer stream

[kleinesfilmroellchen]

The ultimate goal is to make breakwater compatible with my TP-Link Archer C7 router running OpenWRT on mips-unknown-linux-musl (MIPS32, big-endian). This has three main parts:

• Make prometheus exporter into an optional feature. This may be useful for some users who don’t need it, but most importantly, prometheus_exporter doesn’t compile on 32-bit systems since it needs 64-bit atomics. I’m looking forward to Pixelflut on Nintendo 3DS :3
• Fix endianness issues in breakwater (mainly breakwater-parser). Already complete, all relevant tests pass. However, PXMULTI doesn’t work, since it’s fundamentally little-endian. I’ll look into always disabling this feature on big-endian targets. Also, the framebuffer byte order is reversed from little-endian, so each pixel is ordered as RGBA instead of the ABGR on little-endian. This may cause issues with outputs which assume the framebuffer endianness, but I am unable to test any of the existing outputs on that router.
• Add a really simple output protocol which streams the raw framebuffer via UDP (for reception by e.g. ffmpeg). For a low-resolution low-framerate canvas (e.g. 720p with 10fps) this is only 200-300Mbit/s, which will hopefully be fine.
• Add rate-limiting support

[kleinesfilmroellchen]

oops, that was a debugging comment, this should be removed