Problem: vimdoc only covered AtCoder, Codeforces, and CSES, and had no
entries for race, stress, or submit — all of which shipped in this
branch. The platform list was also stale and the workflow example
pointed users to the AtCoder website to submit manually.
Solution: add CodeChef, USACO, and Kattis to the supported platforms
list and platform-specific usage section (including Kattis's
dual single-problem/full-contest behavior). Document :CP stress,
:CP race, and :CP submit in the commands section, add their <Plug>
mappings, and add dedicated STRESS TESTING, RACE, and SUBMIT sections.
Update get_active_panel() to list its return values, add the
cp.race.status() API under the statusline section, and update the
workflow example step 8 to use :CP submit.
Barrett Ruth
52cf54d05c