* Expose trade feed websocket exchange data through data channel
Most relevant to applications that import GCT as a lib, this allows
them to (through configuration, disabled by default) receive trade data
through the data channel similarly to the orderbook feed.
* exchanges: allow exposure of trade websocket feed through data channel
* Expose fill feed websocket abstracted exchange data through data channel
* exchanges: allow exposure of fill websocket feed through data channel
* golangci-lint/CI: Bump versions
Fix remaining linter issues
* Specifically set AppVeyor version
* Fix the infamous typos 👀
* Add go env cmd to AppVeyor
* Add go version cmd to AppVeyor
* Specify AppVeyor image, adjust linters
* Update go get to go install due to deprecation
* Bump golangci-lint timeout time for AppVeyor
* Change NW contract to NQ
* Address nitters
* GetRandomPair -> Pair{}
* Address nits
* Address time nitterinos plus additional tweaks
* More time inception upgrades!
* Bending time and space
* exchanges/ftx: add support for ReduceOnly, ImmediateOrCancel and PostOnly orders
* exchanges/ftx: adapt tests to ReduceOnly/ImmediateOrCancel/PostOnly boolean flags
* exchanges/ftx: wrong json key of WsFillsDataStore.FillsData was causing json.Unmarshal() to yield an empty struct
* exchanges/ftx: update WsFills to latest API
* exchanges/ftx: add TestFTX_wsHandleData_wsFills
* exchanges/ftx: WsOrders.FilledSize was never parsed properly because of a key error (was spelled `filedSize` -- with one L); enrich data structure to support latest API fields
* exchanges/ftx: when order is closed, set status to closed, not canceled
* exchanges/ftx: compatibleOrderVars: compare floats for almost-equality
* order.Detail: add field: AverageExecutedPrice float64
* exchanges/ftx: FTX.wsHandleData() now populates all order.Detail fields properly on update/orders websocket message
* exchanges/ftx: implement TestFTX_wsHandleData_Details()
* exchanges/ftx: make golangci-lint happy
* exchanges/ftx: make golangci-lint happy
* exchanges/ftx/test: delete redundant commented code
* exchanges/ftx: move websocket tests from ftx_test.go to ftx_websocket_test.go
* exchanges/ftx: remove redundant line
* exchange/ftx: greatly simplify TestFTX_wsHandleData (thanks to @shazbert)
* exchanges/ftx: make golangci-lint/whitespace happy
* exchanges/ftx: requested review change: delete a redundant line
* exchanges/ftx/test: use predefined currency constants
