手动实现一个react-router4（部分实现）
- react-router4
- public
- index.html
- manifest.json
- favicon.ico
- hash.html
- history.html
- src
- react-router-dom
- index.js
- HashRouter.js
- Route.js
- context.js
- Link.js
- Redirect.js
- Switch.js
- Home.js
- index.js
- Profile.js
- User.js
- UserAdd.js
- UserList.js
- .gitignore
- package.json
- README.md
- yarn.lock