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/httpput-postfields.c

@@ -43,7 +43,7 @@ static const char olivertwist[]=
    509 byte limit. */
 
 /*
- * This example shows a HTTP PUT operation that sends a fixed buffer with
+ * This example shows an HTTP PUT operation that sends a fixed buffer with
  * CURLOPT_POSTFIELDS to the URL given as an argument.
  */