Expose relative URL fixer filter in Jinja2 environment

[SuibianP]

(Discussed in #199)

MkDocs has the url filter (implemented here and exported here) that resolves relative URLs to the current page. mkdocs-macro has a similar function fix_url which is not exported to the jinja environment.

The direct workaround is adding it to the environment in define_env as mentioned here. Nonetheless, as this functionality is frequently used such as when constructing href attributes, it would be beneficial to export this by default. Preferably the filter could be named url as well to match mkdocs behaviour.

[github-actions]

Welcome to this project and thank you!' first issue

[fralau]

The last version on github now contains that filter, visible thanks to {{ macros_info() }}.

@SuibianP Could I ask you to test whether it works correctly for you?

[SuibianP]

@fralau Thanks for the addition! "relative/url/to/base" | normalize_url(page) works for me now.

Would it be better to take env.page instead of None by default, so that there is no need to repeat page for the most common case (relative to current page)? This is also how url_filter is implemented.

[fralau]

OK, I had missed that point!

Back to the drawing, board. I implemented the new filter, called relative_url, exactly as implemented in the example of the discussion.

[fralau]

@SuibianP Test again?

[SuibianP]

@fralau Works for me, thanks a lot!