Feature: Follow footnote references

[jakewvincent]

Idea: In the following context, CRing on [^footnoteref] would cause the cursor to jump to the line where the footnote is defined (line 4 below).

1 _Foo_, _bar_, and _baz_ may be used as metasyntactic variables.[^footnoteref]
2 ...
3 ...
4 [^footnoteref]: Metasyntactic variables in the domain of computer science are words that are used as
  placeholders or stand-ins for certain kinds of expressions. Read more [here](https://example.org).

[ghost]

This is exactly what I meant in the issue. If you are implementing this feature, do not forget reference links since they behave in a very similar manner.

For example:

_Foo_, _bar_, and _baz_ may be used as [metasyntactic variables].

[metasyntactic variables]: https://example.org

[lyndhurst]

Support for footnotes would be a great addition. I use vim-markdownfootnotes which handles inserting a new footnote definition and return to the footnote reference elegantly, but it lacks navigation for existing ones.

I would also add that some other functionalities could be useful like:

• 'refreshing footnotes numbering',
• some type of completion to easily add a reference to an existing footnote definition while typing.

Thanks a lot for considering this new feature.