GENERIC:

- BUG: SID allocator needs work for supporting the overflow case (1 million connections).

- BUG: A passive client with no 'I4' (or 'I6') flag set,
  cannot set it at any later point.
  I4,I6,U4,U6 cannot be updated!

- BUG?
  No IQUI to disconnected user if they are disconnected by the hub.
  Only peers receive that, but the disconnected user will receive a STA
  (status) message.
  The ADC spec is unclear on this point.

- Some very rare abort or crashes.
  Window hub just stop without actually crashing.
  Seem to be some weird memory race conditions also.

- Exceeding send queue by just joining. Need to use dynamic send queue
  based on number of clients.

- A memory leak in hub_handle_info() -> update_user_info() -> adc_msg_copy().

- Get rid of list.c, use TAILQ instead!

Feature enhancements:
- No support for changing nick names.

Todo:
* Commands
	* !kick_nick <nick>
	* !kick_cid  <cid>
	* !kick_ip   <ip>
	* !reload
	* !stats
	* +myip
	* !help