Hitbtc3 fetchPositions
Hitbtc3 fetchPositions

Added margin functionality to fetchPositions:
```
hitbtc3.fetchPositions ()
2022-03-29T01:20:00.189Z iteration 0 passed in 192 ms

  symbol | notional | marginType | liquidationPrice | entryPrice | unrealizedPnl | percentage | contracts | contractSize | markPrice | side | hedged |     timestamp |                datetime | maintenanceMargin | maintenanceMarginPercentage |    collateral | initialMargin | initialMarginPercentage | leverage | marginRatio
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
BTC/USDT |          |   isolated |                0 |   47435.57 |               |            |           |              |           |      |
   | 1648516584430 | 2022-03-29T01:16:24.43Z |                   |                             | 20.8750800665 |               |
       |       12 |
1 objects
```

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