badwords: rework exceptions, fix many of them

Also:
- support per-directory and per-upper-directory whitelist entries.
- convert badlist input grep tweak into the above format.
  (except for 'And' which had just a few hits.)
- fix many code exceptions, but do not enforce.
  (there also remain about 350 'will' uses in lib)
- fix badwords in example code, drop exceptions.
- badwords-all: convert to Perl.
  To make it usable from CMake.
- FAQ: reword to not use 'will'. Drop exception.

Closes #20886

lib/headers.h

@@ -38,7 +38,7 @@ struct Curl_header_store {
 
 /*
  * Initialize header collecting for a transfer.
- * Will add a client writer that catches CLIENTWRITE_HEADER writes.
+ * Add a client writer that catches CLIENTWRITE_HEADER writes.
  */
 CURLcode Curl_headers_init(struct Curl_easy *data);