tinkr: Cast '(R)Markdown' Files to 'XML' and Back Again

anchored links are processed by default

Code
  show_user(m$show(), force = TRUE)
Output
  ---
  title: this tests links
  ---

  ## These are some links that are valid in basic markdown

  This is some text [that contains links][this fun link1] which
  [can be `inline`](https://example.com/2) or [can be spread across multiple lines
  because the link text is JUST TOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
  LONG, y'all][link3].

  Mainly, we want to see if [link text
  by reference][link4] and if links [can be referenced multiple times][this fun link1]

  This should also [include non-reference links](https://example.com/5)

  If you [write]{.confession} \[some link text\]\[link2\], that will appear as [some link text][link2]
  but you can also [test][racehorse] [sub][sub-link1] [links][sub_link2]

  [pizza \& icecream][pizzaicecream] = fun

  ```markdown
  you can write links like [a link](https://example.com/racehorse) or using
  [reference style][racehorce]

  [racehorse]: https://example.com/racehorse/   
  ```

  ## This is some extended markdown content {#extended .callout}

  This should also include references that use [standalone] links and
  footnotes should not be properly parsed and will be considered 'asis' nodes,
  at least that's what I *believe*[^footy]. Maybe this might not pan out [^but who
  knows? footnotes are **WEIRD**, man].

  <!-- links go here! -->

  [^footy]: this is a footnote that
  should be preserved

  [this fun link1]: https://example.com/1
  [link3]: https://example.com/3
  [link4]: https://example.com/4
  [link2]: https://example.com/2 "link with title!"
  [racehorse]: https://example.com/racehorse/
  [sub-link1]: https://example.com/racehorse/1/1 "One One Won One"
  [sub_link2]: https://example.com/racehorse/2/2/ "Two Two Won One Two"
  [pizzaicecream]: https://example.com/pizza&icecream
  [standalone]: https://example.com/standalone

users can turn off anchor links

Code
  show_user(m$show(), force = TRUE)
Output
  ---
  title: this tests links
  ---

  ## These are some links that are valid in basic markdown

  This is some text [that contains links](https://example.com/1) which
  [can be `inline`](https://example.com/2) or [can be spread across multiple lines
  because the link text is JUST TOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
  LONG, y'all](https://example.com/3).

  Mainly, we want to see if [link text
  by reference](https://example.com/4) and if links [can be referenced multiple times](https://example.com/1)

  This should also [include non-reference links](https://example.com/5)

  If you [write]{.confession} \[some link text\]\[link2\], that will appear as [some link text](https://example.com/2 "link with title!")
  but you can also [test](https://example.com/racehorse/) [sub](https://example.com/racehorse/1/1 "One One Won One") [links](https://example.com/racehorse/2/2/ "Two Two Won One Two")

  [pizza \& icecream](https://example.com/pizza&icecream) = fun

  ```markdown
  you can write links like [a link](https://example.com/racehorse) or using
  [reference style][racehorce]

  [racehorse]: https://example.com/racehorse/   
  ```

  ## This is some extended markdown content {#extended .callout}

  This should also include references that use [standalone](https://example.com/standalone) links and
  footnotes should not be properly parsed and will be considered 'asis' nodes,
  at least that's what I *believe*[^footy]. Maybe this might not pan out [^but who
  knows? footnotes are **WEIRD**, man].

  <!-- links go here! -->

  [^footy]: this is a footnote that
  should be preserved