Main changes:
* irc is now a plugin
* irc: remove kernel info in CTCP VERSION reply
* relay: add relay plugin (network communication between WeeChat and remote
application)
* logger: add logger plugin with new features: backlog, level for messages to
log
* plugins: add some other plugins: alias, demo, fifo, tcl, xfer
* api: new plugin API with many new functions: hooks, buffer management and
nicklist, bars, configuration files, network, infos/infolists, lists, upgrade
* gui: new display engine, with prefix and message for each line
* gui: add new type of buffer, with free content
* gui: fix display bug with some weird UTF-8 chars
* core: improve main loop: higher timout in select(), less CPU usage
* core: new name for configuration files (*.conf instead of *.rc)
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