With the current version, if you open e.g. this page:
https://python-markdown.github.io/reference/markdown/blockprocessors/

The ‹› links on the right side of the page will point to URLs like
https://github.com/Python-Markdown/markdown/tree/3.6//home/runner/work/markdown/markdown/md/markdown/blockprocessors.py

This commit fixes them by replacing `filepath` with `relative_filepath`.

A new `AbbrTreeprocessor` has been introduced, which replaces the now
deprecated `AbbrInlineProcessor`. Abbreviation processing now happens
after Attribute Lists, avoiding a conflict between the two extensions.
Fixes #1460.

The `AbbrPreprocessor` class has been renamed to `AbbrBlockprocessor`, which
better reflects what it is. `AbbrPreprocessor` has been deprecated.

A call to `Markdown.reset()` now clears all previously defined abbreviations.

* `AbbrTreeprocessor` now sorts the abbreviation
list by length before processing the element tree

This ensures that multi-word abbreviations are
implemented even if an abbreviation exists for
one of those component words.

* Added handling for empty abbreviations.

* Added a `glossary` option for the `abbr` extension
which accepts a dictionary.