Improved URL selector handling.
parse_url stores the URL selector in the output_buffer - which is currently 520 bytes. A new entry point called parse_url_buffer was added which instead stores the URL selector in a buffer provided by the user.
url_download now calls the new parse_url_buffer instead of parse_url. The buffer for the URL selector is simply the download_buffer. So the download_buffer is used twice: First to hold the URL selector to be sent as request to the server and then to hold the response received from the server.
However, the URL selector still can't exceed the MSS (aka 1460 bytes).
Note: The User-Agent string was shortened by two bytes as that allows a "default" URL (incl. 'http://' but without port number) of exactly 1400 bytes to end up as 1460 bytes URL selector.
Tweet65 is sample application for triggering an IFTTT maker webhook. If ~450 chars are not enough for the URL then either the IP65 output_buffer needs to be increased or url_parse needs to be modified to use a different buffer. E.g. when called from url_download then the url_download_buffer could be temporarily used to hold the selector.