UTF-8 encode/decode support, from martylake

Based largley on martylake's provided patch set. By default, assumes
all IRC messages are UTF-8 encoded and will translate to CP-437 if
appropriate or send as UTF-8 if the user's terminal supports it.
Set utf8_support=false in the [irc] section of your ctrl/modopts.ini
file if you wish to disable this behavior.