tidy-up: miscellaneous

- gnutls, mbedtls: fix casing in log messages.
- src/tool_cfgable.h: drop unused header.
- appveyor.sh: variable style.
- cmakelint.sh: sync with libssh2, catch `.cmake.in` explicitly.
- examples: drop obsolete comments, exclamation marks.
- fix comment typos, casing.

Closes #19839

docs/examples/anyauthput.c

@@ -150,7 +150,7 @@ int main(int argc, char **argv)
 
     /* tell libcurl we can use "any" auth, which lets the lib pick one, but it
        also costs one extra round-trip and possibly sending of all the PUT
-       data twice!!! */
+       data twice */
     curl_easy_setopt(curl, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
 
     /* set username and password for the authentication */

docs/examples/http2-upload.c

@@ -27,7 +27,7 @@
  */
 #ifdef _MSC_VER
 #ifndef _CRT_SECURE_NO_WARNINGS
-#define _CRT_SECURE_NO_WARNINGS  /* for '_snprintf(), fopen(), localtime(),
+#define _CRT_SECURE_NO_WARNINGS  /* for _snprintf(), fopen(), localtime(),
                                     strerror() */
 #endif
 #endif

docs/examples/simplessl.c

@@ -46,11 +46,6 @@
    4.   if you do not use a crypto engine:
    4.1. set pKeyName to the filename of your client key
    4.2. if the format of the key file is DER, set pKeyType to "DER"
-
-   !! verify of the server certificate is not implemented here !!
-
-   **** This example only works with libcurl 7.9.3 and later! ****
-
 */
 
 int main(void)