Hitbtc3 fetchPosition
Hitbtc3 fetchPosition

Added fetchPosition for swap and margin markets:

Swap
```
hitbtc3.fetchPosition (BTC/USDT:USDT)
2022-04-01T22:58:35.554Z iteration 0 passed in 192 ms

{
  info: {
    symbol: 'BTCUSDT_PERP',
    type: 'isolated',
    leverage: '10.00',
    created_at: '2022-04-01T22:56:03.408Z',
    updated_at: '2022-04-01T22:56:11.833Z',
    currencies: [
      {
        code: 'USDT',
        margin_balance: '7.291188459700',
        reserved_orders: '0',
        reserved_positions: '0.478285714500'
      }
    ],
    positions: [
      {
        id: '3008606',
        symbol: 'BTCUSDT_PERP',
        quantity: '0.0001',
        price_entry: '46300.65',
        price_margin_call: '',
        price_liquidation: '0',
        pnl: '0',
        created_at: '2022-04-01T22:56:03.408Z',
        updated_at: '2022-04-01T22:56:11.833Z'
      }
    ]
  },
  symbol: 'BTC/USDT:USDT',
  notional: undefined,
  marginType: 'isolated',
  liquidationPrice: 0,
  entryPrice: 46300.65,
  unrealizedPnl: undefined,
  percentage: undefined,
  contracts: 0.0001,
  contractSize: undefined,
  markPrice: undefined,
  side: undefined,
  hedged: undefined,
  timestamp: 1648853771833,
  datetime: '2022-04-01T22:56:11.833Z',
  maintenanceMargin: undefined,
  maintenanceMarginPercentage: undefined,
  collateral: 7.2911884597,
  initialMargin: undefined,
  initialMarginPercentage: undefined,
  leverage: 10,
  marginRatio: undefined
}
```

Margin:
```
hitbtc3.fetchPosition (BTC/USDT, [object Object])
2022-04-01T22:58:07.289Z iteration 0 passed in 192 ms

{
  info: {
    symbol: 'BTCUSDT',
    type: 'isolated',
    leverage: '12.00',
    created_at: '2022-04-01T22:15:22.914Z',
    updated_at: '2022-04-01T22:57:44.266Z',
    currencies: [
      {
        code: 'USDT',
        margin_balance: '5.808049920788',
        reserved_orders: '0',
        reserved_positions: '0.164378294750'
      }
    ],
    positions: [
      {
        id: '632422',
        symbol: 'BTCUSDT',
        quantity: '0.00004',
        price_entry: '46303.75',
        price_margin_call: '0',
        price_liquidation: '0',
        pnl: '0',
        created_at: '2022-04-01T22:15:22.914Z',
        updated_at: '2022-04-01T22:57:44.266Z'
      }
    ]
  },
  symbol: 'BTC/USDT',
  notional: undefined,
  marginType: 'isolated',
  liquidationPrice: 0,
  entryPrice: 46303.75,
  unrealizedPnl: undefined,
  percentage: undefined,
  contracts: 0.00004,
  contractSize: undefined,
  markPrice: undefined,
  side: undefined,
  hedged: undefined,
  timestamp: 1648853864266,
  datetime: '2022-04-01T22:57:44.266Z',
  maintenanceMargin: undefined,
  maintenanceMarginPercentage: undefined,
  collateral: 5.808049920788,
  initialMargin: undefined,
  initialMarginPercentage: undefined,
  leverage: 12,
  marginRatio: undefined
}
```

ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt,ccxt/ccxt