bithumb: Add websocket support (#745)

* bithumb: Add websocket support (WIP)

* bithumb: cont impl.

* bithumb: finish, issues with orderbook needs review

* linter issues

* bithumb: move to separate file

* bithumb: change to pointer for book

* bithumb: Add tests

* bithumb: Address nits

* websocket: Export subscription error and wrap returns

* bithumb: cleanup/ fix tests

* gctrpc/bithumb: fix misspelling

* bithumb: gofmt

* readme: update support table, regen doc

* tradesReadme: update

* readme: update template

exchanges/bithumb/convert_test.go

@@ -0,0 +1,27 @@
+package bithumb
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+func TestBithumbTime(t *testing.T) {
+	var newTime bithumbTime
+	err := json.Unmarshal([]byte("bad news"), &newTime)
+	if err == nil {
+		t.Fatal(err)
+	}
+
+	strData := []byte(`"1628739590000000"`) // Thursday, August 12, 2021 3:39:50 AM UTC
+	err = json.Unmarshal(strData, &newTime)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tt := newTime.Time()
+	if tt.UTC().String() != "2021-08-12 03:39:50 +0000 UTC" {
+		t.Fatalf("expected: %s but receieved: %s",
+			"2021-08-12 03:39:50 +0000 UTC",
+			tt.UTC().String())
+	}
+}