swirl 2.4.0

swirl 2.4.0

• Added support for multiple languages, including Spanish, French, German,
  Turkish, Simplified Chinese, and Korean. The default language can be changed
  using the function select_language().
• Added install_course() in order to install swirl courses that are
  distributed in the .swc format.
• The directories where swirl courses and where user data is stored can now be
  explicitly specified. These options can be set using the function
  swirl_options().
• It's now possible to log and collect a student's progression
  through a swirl course. Enable logging with swirl_options().
• Improved support for displaying non-ASCII character sets
  through UTF-8 encoding.
• Now compatible with swirlify::demo_lesson().