feat:企业微信-电子发票 (#695)

Co-authored-by: markwang <www.wang61@qq.com>

work/invoice/client.go

@@ -0,0 +1,17 @@
+package invoice
+
+import (
+	"github.com/silenceper/wechat/v2/work/context"
+)
+
+// Client 电子发票接口实例
+type Client struct {
+	*context.Context
+}
+
+// NewClient 初始化实例
+func NewClient(ctx *context.Context) *Client {
+	return &Client{
+		ctx,
+	}
+}