to bring CAIP-25 draft text up to date

[bumblefudge]

If merged, this would supersede #108 (see for older discussions) and also closes #142

[bumblefudge]

open question, raised by @FrederikBolding : should the RPC call nest each of these provider objects named after namespaces into a parent array between params and eip155/cosmos/etc? i.e.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "provider_authorization",
  "params": {
    "namespaces": {
      "eip155": {
        "chains": [
          "eip155:1"
        ],
        "methods": [
          "eth_sendTransaction",
          "eth_signTransaction",
          "eth_sign",
          "personal_sign"
        ],
        "events": [
          "accountsChanged",
          "chainChanged"
        ]
      },
      "cosmos": {}
    }
  }
}