[Bug] some `crossref` options do not work for pdf format

[juliantao]

It seems that some of the crossref options do not work for pdf formats.

I included the following in the YAML header:

crossref:
  fig-title: "**Figure**"
  tbl-title: "**Table**"
  title-delim: "."
  fig-prefix: Fig.
  tbl-prefix: Table

When rendered to html, all the options work properly.

For pdf output, the fig-prefix and tbl-prefix were rendered as expected, but the fig-title, tbl-title, and title-delim were still rendered with default formats.

[jjallaire]

Since LaTeX takes care of formatting the table and figure captions directly, we need to communicate these settings to LaTeX as follows:

\AtBeginDocument{%
\renewcommand*\figurename{Figure}
\renewcommand*\tablename{Table}
}

We can't readily pass formatting directives to these macros (see https://tex.stackexchange.com/questions/82993/how-to-change-the-name-of-document-elements-like-figure-contents-bibliogr)

We also don't currently attempt to forward delimiters to LaTeX although I just noted here (http://www.peteryu.ca/tutorials/publishing/latex_captions) that this is indeed possible.

These limitations were unfortunately not documented --- I've just remedies this. Will also keep this issue open as I think there is definitely more we should be doing here.

[mcanouil]

FYI, it's still happening in current 1.3 pre-release, at least for title-delim.
I think it would be good to put this for 1.4 milestone (probably a bit late for 1.3).

• *-prefix options seem to work as intended in both formats.
• Formatting in *-title options does work only in html formats.
• title-delim option only works in html formats.

---
format:
  pdf: default
  html: default
crossref:
  fig-title: "**Figure**"
  tbl-title: "**Table**"
  title-delim: "."
  fig-prefix: Fig.
  tbl-prefix: Tab.
---

```{r}
#| label: fig-fig
#| fig-cap: plot
plot(pressure)
```

```{r}
#| label: tbl-table
#| tbl-cap: table
knitr::kable(head(iris))
```

@fig-fig

@tbl-table