countdown 0.4.0

Release Post: countdown v0.4.0 – Now on CRAN!

New Features

{countdown} now uses {prismatic} for color calculations.
The JavaScript implementation of countdown has been completely rewritten. It
now supports a wide range of new interactions:
- Start, pause, and reset the timer (click, click again, double click).
- + or - buttons to bump timer up or down.
- Keyboard shortcuts: Space/Enter to start/stop, Escape to reset, and up/down
  arrows to bump timer.
- The timers now work on mobile devices (in particular in xaringan slides).
countdown timers can now be used in or controlled by Shiny apps:
- Use countdown_update() to update key initial timer settings.
- Use countdown_action() to trigger common action: start, stop, reset,
  bump up or bump down.
- State changes are reported back to the Shiny app, e.g. Shiny apps can
  use input$timer to receive event data from the timer with
  id = "timer".
- countdown_shiny_example() runs a Shiny app that demonstrates key
  Shiny app features.
Timers can now start immediately by setting the argument
start_immediately = TRUE. When TRUE, timers will start as soon as they
are visible. This feature works in xaringan slides, Quarto slides and general
HTML web pages (thanks @Dr-Joe-Roberts, @davidkane9, #12).
The countdown_app() now supports bookmarking, making it possible to share
pre-configured timer URLs. This feature improves the usability of the
timer available at https://apps.garrickadenbuie.com/countdown.