misc: typo and grammar fixes

- Replace `Github` with `GitHub`.
- Replace `windows` with `Windows`
- Replace `advice` with `advise` where a verb is used.
- A few fixes on removing repeated words.
- Replace `a HTTP` with `an HTTP`

Closes #9802

docs/examples/http-post.c

@@ -40,7 +40,7 @@ int main(void)
   curl = curl_easy_init();
   if(curl) {
     /* First set the URL that is about to receive our POST. This URL can
-       just as well be a https:// URL if that is what should receive the
+       just as well be an https:// URL if that is what should receive the
        data. */
     curl_easy_setopt(curl, CURLOPT_URL, "http://postit.example.com/moo.cgi");
     /* Now specify the POST data */