add middleware to force trailing slash or to remove trailing slash

[prabirshrestha]

Similar to https://echo.labstack.com/middleware/trailing-slash/.

Some blog sites forces trailing slash and some doesn't. In order to maintain SEO as I move moved from an old blog framework I would like to force trailing slash or remove it.

Forcing trailing slash also makes markdown just work for blogs. For those navigating to http://localhost:8080/posts/welcome/ with the welcome/article.md one could write ![image](image.png) which is in welcome/image.png folder and it would correctly render the image http://localhost:8080/posts/welcome/image.png.

[chrislearn]

Done

[prabirshrestha]

This works. Though I think it should be named trailing_slash instead of tailing_slash.

[prabirshrestha]

Thanks for renaming it to trailing_slash.

This is now working as expected.