# URL SHORTREN
1. No matter user sign in or not, user can create short url.
2. User can customize link by alias
1. alias is nil, system will generate four digits number
2. alias duplicated, show error message.
3. alias is unique, create short url by alias, like localhost:3000/gem_camp
4. It has a button for copy short url(clipboard)
3. User sign in and create shorturl , user can view how many short url created.
4. User can delete their short url(soft kill).
5. You need to counter how many views in this short url, record ip and user agent. calc how many percent of model client and PC client.
6. User can export short url list by csv.

## bonus
1. User not sign in, still can see the url list they created. You can finish this feature by cookie.
2. Add a button in the create page , user can check the alias is avaialbe or not.(by sitmulusJS)
## example