TODO


* Input is URL/URLs for rightmove search. URL/URLs are passed as positional
  arguments to main binary. Same way as for curl or wget tools.
* Binary can run forever or just once (--once option).
* There is an --interval option to control fetch frequency.
* After each iteration binary will dump "seen" set as a JSON.
* Option to specify a path to seen list file.


GENERAL ALGORITHM

* Fetch URL.
* Parse flats into slice of structs.
* Remove already seen flats.
* Send new flats to telegram. One message per each flat?
* Add new flats to seen list.
* Remove out of retention flats from seen list to prevent it from growing
  indefinitely.