Use CSS variables and static html dependency

[gadenbuie]

This PR rewrites countdown's CSS to use CSS variables rather than the previous whisker template. This has a number of advantages, but results in a large breaking change.

1. We now can use html_dependency_countdown(), a static html dependency. Previously the css was a template and the dependency was re-written dynamically with each render, which causes problems and obviously can't be used for Quarto. This fixes the issue mentioned here: quarto shortcode #27 (comment)

2. The breaking change is that the first countdown() no longer styles the other timers. In retrospect this is a bug masquerading as a feature 😄 Now, users need to separately call style_countdown() to globally style the countdown timers.

3. I've kept all of the same arguments in countdown() but they all default to NULL now. style_countdown() is documented in the same page so that the arguments and functions are collocated.

Fixes #28
Fixes #34
Incidentally fixes #30

[coatless]

LGTM! 👍

Only a minor note on the style_countdown() function.

Please merge when ready. I'll spin up a second PR for the re-org. (Or, if you'd like I can wait until the #37 is complete.)

[coatless]

To match with other function names in the package, maybe go:

countdown_styler()

instead of:

style_countdown()

[gadenbuie]

Thanks for calling this out. style_{thing} is a pattern I tend to follow across my projects, even though it breaks the usual prefixing rules. In Shiny/html land, I tend to prefer a verb-first approach to separate between functions that create UI and functions for interactivity.

For example, looking at this list I'd prefer update_countdown() and style_countdown(), since in Shiny we group update_ functions and in my packages I use style_ for prefixes.

The problem -- and the reason I didn't use update_countdown() when I wrote it -- is countdown_action(). I can't think of a good name for that function. The other best option I've come up with is trigger_countdown(), which I don't like enough to use. So, IIRC, I went with countdown_update() for internal consistency.

So, on the whole, I agree and think countdown_style() is probably the best option.

[coatless]

@gadenbuie We can also use this as an opportunity to rename functions if you wish. Redirects can be setup for backward compatibility with lifecycle.

[coatless]

This is a really elegant and concise way of setting the CSS variables.

[gadenbuie]

Thanks! Sometimes it pays to be lazy (and to be consistent in naming things) 😉

[coatless]

I'm going to go ahead and merge this PR.

I'll rebase #37 and, then, I'll start the re-org.