add transfer id and sub account cross margin balances

porfolio margin account support

flash swap api; missing fields in futures auto order; wallet sub acco…

…unt balances

spot candles suport 30d

futures delivery candlesticks support more intervals

add withdrawl and deposit fee; add spot currency fixed rate

add options API and currency chains API

spot public trades supports time range query

update documents

release 5.21.5

1. You can set currency_pair as empty string for finished orders or trades query
2. Add margin and cross margin max transferable API support
3. Add futures position closes history query with time range support
4. Add withdraw fees on multiple chains