Reuse epoxy chunks

[gadenbuie]

This PR adds a helper function to make it easier to reuse epoxy chunks as templates throughout a document.

```{epoxy movie-release}
{.emph title} was released in {year}.
```

```{r}
# Re-using the template we defined above
epoxy_use_chunk(bechdel[1, ], "movie-release")
```

```{r}
# Using in a dplyr pipeline
bechdel |>
  dplyr::filter(year == 1989) |>
  epoxy_use_chunk("movie-release")
```

Or you could even call it inline:

> `r epoxy_use_chunk(bechdel[2, ], "movie-release")`

📖 Preview the docs: http://pkg.garrickadenbuie.com/epoxy/preview/pr106/reference/epoxy_use_chunk.html

Name

I initially called this function epoxy_template_chunk(), but as I started to write the docs and setup pkgdown I've realized that I use the word template throughout epoxy. I think it's still correct – I use template to mean the text with the {.emph title} strings – but it might be clearer with another naming convention. I also envision another function that uses templates stored in files, so we need to accomodate at least a _file suffix.

Here are some other ideas I considered:

• epoxy_reuse_chunk()
• 🥇 epoxy_use_chunk()
• epoxy_with_chunk()
• epoxy_from_chunk()
• epoxy_render_chunk()

After sitting on this for a bit, I've decided to go with epoxy_use_*() as the prefix, as in epoxy_use_chunk() and epoxy_use_file(). In addition to being the shortest function name, it's also a reasonable explanation of what happens. You aren't re-using just the template itself, you're also using all of the settings from the chunk (or from the file when that's implemented).

TODO

• Choose final name: epoxy_use_chunk()
• Is chunk option ordering correct?
  • function call > current chunk > template chunk > global chunk options (via current chunk)
  • The "current chunk" options are only the options explicitly set on the current chunk
  • Global chunk options container the current chunk opts (there's no other way), but that's okay.
• Finish description
• Add tests
• NEWS

[github-actions]

📕 Preview documentation for this PR has been cleaned up.

[codecov-commenter]

Codecov Report

Merging #106 (876baef) into main (089e6d8) will increase coverage by 0.23%.
The diff coverage is 100.00%.

❗ Current head 876baef differs from pull request most recent head 4bc2a61. Consider uploading reports for the commit 4bc2a61 to get more accurate results

@@            Coverage Diff             @@
##             main     #106      +/-   ##
==========================================
+ Coverage   95.71%   95.94%   +0.23%     
==========================================
  Files           9       11       +2     
  Lines         886      938      +52     
==========================================
+ Hits          848      900      +52     
  Misses         38       38              

Files Changed	Coverage Δ
R/engines.R	94.15% <100.00%> (+0.03%)	⬆️
R/epoxy_use_chunk.R	100.00% <100.00%> (ø)
R/transformers.R	100.00% <100.00%> (ø)
R/utils-knitr.R	100.00% <100.00%> (ø)