tidy-up: miscellaneous

- fix typos and wording in documentation and comments.
- KNOWN_BUGS: merge duplicate H1 section.
- test_10_proxy: delete stray expressions.
- Perl: `while()` -> `while(1)`.
- Perl: fix indent, whitespace, drop redundant quotes and parentheses.
- fix casing: URL, SSL, Windows.
- badwords: readd `threadsafe`, add `well-known` (and fix it).
- replace `WinXP` -> `Windows XP` to match other uses.

Closes #21646

src/tool_doswin.c

@@ -549,7 +549,7 @@ SANITIZEcode sanitize_file_name(char ** const sanitized, const char *file_name,
  *  4. Windows Directory (e.g. C:\Windows)
  *  5. all directories along %PATH%
  *
- * For WinXP and later search order actually depends on registry value:
+ * For Windows XP and later search order actually depends on registry value:
  * HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\SafeProcessSearchMode
  */
 CURLcode FindWin32CACert(struct OperationConfig *config,