Initial Support for More Quarto-like Cell Options

[coatless]

From the Quarto Code Cell: Knitr documentation, there are quite a few different options to support on a per-cell basis. The following lays out what I think would be a good set of initial options to support for a more R like Quarto experience in the browser.

If I'm missing something from here, please feel free to comment below.

Attributes

The attributes portion will likely be useful for allowing custom CSS classes to be applied to the code cell.

We're also interested in having a label being available. Though, we're probably not going to want to override our initial ID structure.

Option	Description
label	Unique label for code cell. Used when other code needs to refer to the cell
classes	Classes to apply to cell container

Code Evaluation

This is probably a stretch for now outside of mapping echo: false over to context: output.

Option	Description
eval	Evaluate code cells (if false just echos the code into output).
``	true (default): evaluate code cell
``	false: don’t evaluate code cell
``	[...]: A list of positive or negative line numbers to selectively include or exclude lines (explicit inclusion/excusion of lines is available only when using the knitr engine)
echo	Include cell source code in rendered output.
``	true (default): include source code in output
``	false: do not include source code in output
``	fenced: in addition to echoing, include the cell delimiter as part of the output.
``	[...]: A list of positive or negative line numbers to selectively include or exclude lines (explicit inclusion/excusion of lines is available only when using the knitr engine)

Cell Output

Differentiating the cell output will be tricky as we do not track conditions (captureConditions: false) when using captureR.

With that in mind, we already have a request in #104, and in #115 we had an attempt to escape HTML entities with output:

Option	Description
output	Include the results of executing the code in the output. Possible values:
``	true: Include results.
``	false: Do not include results.
``	asis: Treat output as raw markdown with no enclosing containers.
warning	Include warnings in rendered output.
error	Include errors in the output (note that this implies that errors executing code will not halt processing of the document).
message	Include messages in rendered output.

Figures

Initial support should likely make available the existing width and height variables

Option	Description
fig-width	Default width for figures
fig-height	Default height for figures

[coatless]

Skipped implementing echo/eval and error.

Added label, classes, fig-cap, out-width, out-height, and dpi.