Update polkadot CAIP-2 and CAIP-10 for XCM v3

[bumblefudge]

Thanks to @ntn-x2 for point out the new GenesisHash function in xcm v3 , and patiently explaining to me the problems with existing CAIP-2 spec!

I merged the existing draft to allow @ntn-x2 to take the pen on an overhaul PR, which as I currently understand it needs the following issues addressed:

• [ ] when more detailed xcm v3 docs go live, update links in readme.md
• [ ] are there any chains that cannot be addressed by genesis hash?
• [ ] should there be a section warning people about migrations? does losing a parachain auction or changing id and restarting as mentioned by joe create a new CAIP-2? if there is any way to find out from a node about a previous NetworkID/CAIP-2 it might be worth mentioning here since the target audience may never have thought about these corner-cases
• [ ] Given that 32 char CAIP-2s are allowed, would it make sense to use the whole genesis hash instead of truncating it? it feels like translating to and from absolute-referenced CAIP-2s to relative-referenced Multilocations would necessitate being able to define NetworkID as ByGenesis, so having the whole one might be needed.