v0.3.0

• Made the course module a public library that can be used to build courses
  in other applications.
• Added rayon-based parallelism, and another optimization that reduced
  allocations. This doesn't change performance much for smaller, typical-size
  courses like sample cptr004.gpx, which currently processes in about 9ms on
  my 13th gen Intel laptop. But the stress test cptr006.gpx with -t 1000
  improves from around 240ms to 65ms with these changes.
• Added a CLI option to specify FIT sport.
• Breaking change: Removed the floor feature for simplicity. That
  optimization is now always in use.