Compatibility:
- Don't use a script-local function to update the format strings
- Protect against `:normal!' moving the cursor on on the wordcount check
Bugfix:
- Let to_string() try to return something for all values
- Now returns correctly when passed both 0 and '0'
Upkeep:
- Simplify check again no valid key from winwidth()
- Old wordcount check: use matchstr() - more expressive and fewer steps
- Improve documentation style/clarity/detail
264c1fefd2