Incorporate relative_url filter in link tag

[ashmaroli]

Resolves #5682
Closes #5943

With this, {% link about.md %} will return /blog/about/ for a site configured with
baseurl: /blog and permalink: pretty

BREAKING-CHANGE

• Initial implementation
• Unit test/ Cucumber feature
  Documentation

[pathawks]

I like this.
This could break just about every site that uses Jekyll.

[ashmaroli]

This could break just about every site that uses Jekyll.

Yes, hence the big red label 😉
Alternatively, we can release this as a new tag entirely..

[pathawks]

Alternatively, we can release this as a new tag entirely..

No, I agree that it should be a clean break.

I wonder about an automated migration assistant. 🤔

[ashmaroli]

I wonder about an automated migration assistant.

Jekyll::Doctor would like to hire an intern to help.. 😁

[DirtyF]

At least breaking changes should be displayed in the post-install message.

[ghost]

I agree with @DirtyF here, let's keep this in mind.

[ashmaroli]

@DirtyF @oe Why not just print the link to our Migration docs since there are going to be numerous breaking-changes..?

[DirtyF]

@ashmaroli of course we'll link to our migration guide. It's just that links are so common that it's the number one thing that's gonna break user's websites, people should know about this, even before considering migrating.

[ghost]

@ashmaroli Let's merge this! Could you add a short post-install message?

[DirtyF]

@jekyllbot: merge +major