Finish implementation of clipboard writing

tools/utils/mimetypes.go

@@ -0,0 +1,24 @@
+// License: GPLv3 Copyright: 2022, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package utils
+
+import (
+	"fmt"
+	"mime"
+	"path/filepath"
+)
+
+var _ = fmt.Print
+
+func GuessMimeType(filename string) string {
+	ext := filepath.Ext(filename)
+	mime_with_parameters := mime.TypeByExtension(ext)
+	if mime_with_parameters == "" {
+		return mime_with_parameters
+	}
+	ans, _, err := mime.ParseMediaType(mime_with_parameters)
+	if err != nil {
+		return ""
+	}
+	return ans
+}