调整项目结构,factory只负责暴露方法，不实现业务细节

docs/README.md

@@ -57,12 +57,24 @@ CREATE TABLE users (id BIGINT PRIMARY KEY AUTO_INCREMENT, ...);
 
 #### 日期转换
 
-```go
-import "git.toowon.com/jimmy/go-common/datetime"
+**推荐方式：通过 factory 使用（黑盒模式）**
 
-datetime.SetDefaultTimeZone(datetime.AsiaShanghai)
-now := datetime.Now()
-str := datetime.FormatDateTime(now)
+```go
+import "git.toowon.com/jimmy/go-common/factory"
+
+fac, _ := factory.NewFactoryFromFile("config.json")
+now := fac.Now("Asia/Shanghai")
+str := fac.FormatDateTime(now)
+```
+
+**或者直接使用 tools 包：**
+
+```go
+import "git.toowon.com/jimmy/go-common/tools"
+
+tools.SetDefaultTimeZone(tools.AsiaShanghai)
+now := tools.Now()
+str := tools.FormatDateTime(now)
 ```
 
 #### HTTP响应（Handler黑盒模式）