HELLOHandshake: report server info and switch RESP protocol version (2 or 3).
| 構文 | HELLO [protover] |
| グループ | connection |
| 引数の数 | -1 |
| 導入バージョン | 1.0.0 |
| フラグ | readonly |
| 計算量 | O(1) |
| Redis 互換性 | differs: only HELLO [2|3] is honoured — the AUTH and SETNAME tails are parsed off and ignored, because kevy has no AUTH and this form does not set the connection name |