added gotch.CleanCache API

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+- Added `gotch.CleanCache()` API.
 
 ## [Nofix]
 - ctype `long` caused compiling error in MacOS as noted on [#44]. Not working on linux box.

file-util.go

@@ -287,3 +287,14 @@ func copyFile(src, dst string) error {
 	_, err = io.Copy(destination, source)
 	return err
 }
+
+// CleanCache removes all files cached at `CacheDir`
+func CleanCache() error {
+	err := os.RemoveAll(CacheDir)
+	if err != nil {
+		err = fmt.Errorf("CleanCache() failed: %w", err)
+		return err
+	}
+
+	return nil
+}