Coinex createMarginLoan, repayMarginLoan
Coinex createMarginLoan, repayMarginLoan

Created repayMarginLoan and createMarginLoan unified methods:

createMarginLoan:
```
node examples/js/cli coinex createMarginLoan USDT BTC/USDT 100

coinex.createMarginLoan (USDT, BTC/USDT, 100)
2022-06-09T07:50:16.625Z iteration 0 passed in 531 ms

{
  id: 2642934,
  currency: 'USDT',
  amount: 100,
  timestamp: undefined,
  datetime: undefined,
  info: { loan_id: 2642934 }
}
```

repayMarginLoan:
```
node examples/js/cli coinex repayMarginLoan USDT BTC/USDT 100

coinex.repayMarginLoan (USDT, BTC/USDT, 100)
2022-06-09T07:51:47.747Z iteration 0 passed in 505 ms

{
  id: undefined,
  currency: 'USDT',
  amount: 100,
  timestamp: undefined,
  datetime: undefined,
  info: { code: 0, data: null, message: 'Success' }
}
```

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