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.go

@@ -0,0 +1,31 @@
+package bithumb
+
+import (
+	"encoding/json"
+	"strconv"
+	"time"
+)
+
+// bithumbMSTime provides an internal conversion helper for microsecond parsing
+type bithumbTime time.Time
+
+// UnmarshalJSON implements the unmarshal interface
+func (t *bithumbTime) UnmarshalJSON(data []byte) error {
+	var timestamp string
+	if err := json.Unmarshal(data, &timestamp); err != nil {
+		return err
+	}
+
+	i, err := strconv.ParseInt(timestamp, 10, 64)
+	if err != nil {
+		return err
+	}
+
+	*t = bithumbTime(time.Unix(0, i*int64(time.Microsecond)))
+	return nil
+}
+
+// Time returns a time.Time object
+func (t bithumbTime) Time() time.Time {
+	return time.Time(t)
+}