subscriptions: Add templating support and integrate with Binance (#1568)

* Subscriptions: Add List.AssetPairs

* Subscriptions: Add Template and QualifiedChannel

These fields separate the concept of what the channel is from the
qualified resource name

* Subscriptions: Add List.SetStates()

* Subscriptions: Add List.QualifiedChannels

* Subscriptions: Rename testsubs.EqualLists

* Binance: Switch to ExpandTemplates

* Binance: Update ConfigTest format

* Subscriptions: Test Coverage improvements

* Subscriptions: Reenterant List.ExpandTemplates

* Subscriptions: Move templates from subscriptions to exchanges

* Binance: Inline subscription template and improvements

exchanges/subscription/README.md

@@ -0,0 +1,72 @@
+# GoCryptoTrader package Subscription
+
+<img src="/common/gctlogo.png?raw=true" width="350px" height="350px" hspace="70">
+
+
+[![Build Status](https://github.com/thrasher-corp/gocryptotrader/actions/workflows/tests.yml/badge.svg?branch=master)](https://github.com/thrasher-corp/gocryptotrader/actions/workflows/tests.yml)
+[![Software License](https://img.shields.io/badge/License-MIT-orange.svg?style=flat-square)](https://github.com/thrasher-corp/gocryptotrader/blob/master/LICENSE)
+[![GoDoc](https://godoc.org/github.com/thrasher-corp/gocryptotrader?status.svg)](https://godoc.org/github.com/thrasher-corp/gocryptotrader/exchanges/subscription)
+[![Coverage Status](http://codecov.io/github/thrasher-corp/gocryptotrader/coverage.svg?branch=master)](http://codecov.io/github/thrasher-corp/gocryptotrader?branch=master)
+[![Go Report Card](https://goreportcard.com/badge/github.com/thrasher-corp/gocryptotrader)](https://goreportcard.com/report/github.com/thrasher-corp/gocryptotrader)
+
+
+This subscription package is part of the GoCryptoTrader codebase.
+
+## This is still in active development
+
+You can track ideas, planned features and what's in progress on this Trello board: [https://trello.com/b/ZAhMhpOy/gocryptotrader](https://trello.com/b/ZAhMhpOy/gocryptotrader).
+
+Join our slack to discuss all things related to GoCryptoTrader! [GoCryptoTrader Slack](https://join.slack.com/t/gocryptotrader/shared_invite/enQtNTQ5NDAxMjA2Mjc5LTc5ZDE1ZTNiOGM3ZGMyMmY1NTAxYWZhODE0MWM5N2JlZDk1NDU0YTViYzk4NTk3OTRiMDQzNGQ1YTc4YmRlMTk)
+
+# Exchange Subscriptions
+
+Exchange Subscriptions are streams of data delivered via websocket.
+
+GoCryptoTrader engine will subscribe automatically to configured channels.
+A subset of exchanges currently support user configured channels, with the remaining using hardcoded defaults.
+See configuration Features.Subscriptions for whether an exchange is configurable.
+
+## Templating
+
+Exchange Contributors should implement `GetSubscriptionTemplate` to return a text/template Template.
+
+Exchanges are free to implement template caching, a map or a mono-template, inline or file templates.
+
+The template is provided with a single context structure:
+```go
+  S              *subscription.Subscription
+  AssetPairs     map[asset.Item]currency.Pairs
+  AssetSeparator string
+  PairSeparator  string
+```
+
+Subscriptions may fan out many channels for assets and pairs, to support exchanges which require individual subscriptions.  
+To allow the template to communicate how to handle its output it should use the provided separators:
+- AssetSeparator should be added at the end of each section related to assets
+- PairSeparator should be added at the end of each pair
+
+We use separators like this because it allows mono-templates to decide at runtime whether to fan out.
+
+See exchanges/subscription/testdata/subscriptions.tmpl for an example mono-template showcasing various features
+
+Templates do not need to worry about joining around separators; Trailing separators will be stripped automatically.
+
+
+## Contribution
+
+Please feel free to submit any pull requests or suggest any desired features to be added.
+
+When submitting a PR, please abide by our coding guidelines:
+
++ Code must adhere to the official Go [formatting](https://golang.org/doc/effective_go.html#formatting) guidelines (i.e. uses [gofmt](https://golang.org/cmd/gofmt/)).
++ Code must be documented adhering to the official Go [commentary](https://golang.org/doc/effective_go.html#commentary) guidelines.
++ Code must adhere to our [coding style](https://github.com/thrasher-corp/gocryptotrader/blob/master/doc/coding_style.md).
++ Pull requests need to be based on and opened against the `master` branch.
+
+## Donations
+
+<img src="https://github.com/thrasher-corp/gocryptotrader/blob/master/web/src/assets/donate.png?raw=true" hspace="70">
+
+If this framework helped you in any way, or you would like to support the developers working on it, please donate Bitcoin to:
+
+***bc1qk0jareu4jytc0cfrhr5wgshsq8282awpavfahc***