Batch RPC call

[shuse2]

Description

Allow caller of RPC to send the request in batch.
It should accept

[
  {
    "jsonrpc": "2.0",
    "method": "message@create",
    "params": "...",
    "id": 1
  },
  {
    "jsonrpc": "2.0",
    "method": "message@create",
    "params": "...",
    "id": 2
  }
]

and it should response as

[
  {
    "id": "1",
    "result": "pong",
    "jsonrpc": "2.0"
  },
  {
    "id": "2",
    "result": "pong",
    "jsonrpc": "2.0"
  }
]

Motivation

If we have multiple small rpc endpoints, calling one by one will be inefficient for network traffic.