Coinex fetchFundingHistory
Coinex fetchFundingHistory

Added the fetchFundingHistory method to Coinex:
```
coinex.fetchFundingHistory (BTC/USDT:USDT)
2022-04-23T16:46:37.381Z iteration 0 passed in 284 ms

       symbol | code |     timestamp |                 datetime |       id |            amount
----------------------------------------------------------------------------------------------
BTC/USDT:USDT | USDT | 1650729623933 | 2022-04-23T16:00:23.933Z | 62052321 |  -0.0095688273996
BTC/USDT:USDT | USDT | 1650700822278 | 2022-04-23T08:00:22.278Z | 62052321 | -0.00625367476584
2 objects
```

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