misc: nitpick grammar in comments/docs

because the 'u' in URL is actually a consonant *sound* it is only
correct to write "a URL"

sorry this is a bit nitpicky :P

https://english.stackexchange.com/questions/152/when-should-i-use-a-vs-an
https://www.techtarget.com/whatis/feature/Which-is-correct-a-URL-or-an-URL

Closes #9699

docs/examples/ftp-wildcard.c

@@ -79,7 +79,7 @@ int main(int argc, char **argv)
 
   /* curl_easy_setopt(handle, CURLOPT_VERBOSE, 1L); */
 
-  /* set an URL containing wildcard pattern (only in the last part) */
+  /* set a URL containing wildcard pattern (only in the last part) */
   if(argc == 2)
     curl_easy_setopt(handle, CURLOPT_URL, argv[1]);
   else

docs/libcurl/curl_escape.3

@@ -33,7 +33,7 @@ char *curl_escape(const char *url, int length);
 .SH DESCRIPTION
 Obsolete function. Use \fIcurl_easy_escape(3)\fP instead!
 
-This function will convert the given input string to an URL encoded string and
+This function will convert the given input string to a URL encoded string and
 return that as a new allocated string. All input characters that are not a-z,
 A-Z or 0-9 will be converted to their "URL escaped" version (\fB%NN\fP where
 \fBNN\fP is a two-digit hexadecimal number).

lib/base64.c

@@ -47,7 +47,7 @@
 static const char base64[]=
   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
 
-/* The Base 64 encoding with an URL and filename safe alphabet, RFC 4648
+/* The Base 64 encoding with a URL and filename safe alphabet, RFC 4648
    section 5 */
 static const char base64url[]=
   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_";

lib/urlapi.c

@@ -116,7 +116,7 @@ static const char *find_host_sep(const char *url)
 }
 
 /*
- * Decide in an encoding-independent manner whether a character in an
+ * Decide in an encoding-independent manner whether a character in a
  * URL must be escaped. The same criterion must be used in strlen_url()
  * and strcpy_url().
  */