[2.0] Update protocol spec documentation

[jlu5]

Some of the things that need to be mentioned:

• The old Irc and Protocol classes were merged together in 2.0, meaning that there is now only one connect() function in each class
  • IRCd protocol modules that used to define connect() now define post_connect() to prevent a name collision (this is an API breaking change!)
• 2.0 protocol modules should now inherit from either classes.IRCNetwork, classes.PyLinkNetworkCoreWithUtils, or protocols.ircs2s_common.IRCCommonProtocol based on how much separation is needed
  • XXX: elaborate more on this
• Renamed members:
  • spawnClient → spawn_client
  • spawnServer → spawn_server
  • updateClient → update_client
  • topicBurst → topic_burst
  • connect → post_connect
  • ping → _ping_uplink (also updated args)
• Mention specific lists that need to be enumerated
  • On connect, add the user to its servers' user list; this is needed for SQUIT handling
  • On JOIN, add the user to the channels' user list AND the channel to the users' channel list - plugins implicitly depend on this consistency in various places