* Update Bittrex API from v1.1 to v3
V1.1 has been retired as of 9/30/2020
- Update REST to V3
- Add initial websocket support
* Bittrex update - enable websockets in testdata config file
* Update Bittrex - add Websocket capability to docs
* Update Bittrex connector
- AppVeyor warnings
- Update tests
- Generate documentation
- Fix nits
* Update Bittrex - add websocket order processing
* Update Bittrex connector
* Bittrex connector - fix ineffectual err assignment
* Fix nits
* Orderbook synchronization
* Remove redundant nil
* Log WS fetch orderbook message as debug message instead of as warning
* Update after rebase
* Add tests
* Add allowed candle interval values
* Replace literals with declared constants
* Replace variable name 'request' with 'req'
* Add check and update for deprecated REST URL
* Nits and some cleaning up
* Change ParseInt bit size to 64
* [FIX] Remove several shadow declarations
* Do not export constructTicker
* Remove parseTime()
* Update GetHistoricCandles()
* [FIX] Address gocritic nits
* [FIX] Address gocritic nits
* Use SendMessageReturnResponse() instead of local map
* Rate limit subscribing and unsubscribing
* [FIX] use go routine for subscribing and unsubscribing
* [FIX] Set correct index for map
* [FIX] Address unused vars, literals, time format
* Adjusted timing when subscribing to many order books
* Cache partial updates to tickers instead of calling REST function
* [FIX] Update sequence nr when multiple updates are queued
* Address golint issues
* Fix nits
